Lake Athabasca

The contents of this online version has not been altered or modified from the original 1990 publication. It is reasonable to assume that much of the data e.g. water levels, camp grounds/boat launches, etc. is out of date. For updated or additional information on any of the lakes in this atlas please go to Environment Alberta's water web site.

Basic Info
Map Sheets74L, M, N, O
Lat / Long59.0238000, -110.3951061
59°1'N, 110°23'W
Area7,770 km2
Max depth124 m
Mean depth20.0 m
Dr. Basin Area282,000 km2
Dam, WeirWeir
Drainage BasinLake Athabasca Basin
Camp GroundPresent
Boat LaunchPresent
Sport FishLake Whitefish, Walleye, Yellow Perch, Arctic Grayling, Northern Pike, Lake Trout
Trophic StatusOligotrophic-Mesotrophic
TP xMain: 12 µg/L
CHLORO xMain: 1.1 µg/L
TDS xMain: 50 mg/L
18
Photo credit: L. Noton

Introduction

Lake Athabasca is Canada's eighth largest lake. The area near the lake supports a wealth of fur-bearing animals, small and large game, dense flocks of waterfowl, and an abundance of fish. These rich resources drew Indians and, later, fur traders to the area. The lake was very important during the fur-trade era and, for a time, it became the centre of conflict between the Hudson's Bay Company and the North West Company. The Peace-Athabasca Delta, located at the southwest end of the lake, is one of North America's major wetlands, and ranks as one of the most biologically productive areas in the world. It is internationally recognized for its importance as a waterfowl production and staging area.

Approximately 30% of Lake Athabasca lies within Alberta and the remainder is located in Saskatchewan. The southwest tip of the lake is situated about 210 km north of the city of Fort McMurray. Lake Athabasca is not easily accessible by road. From the south, Highway 63 extends from Fort McMurray to the hamlet of Fort McKay, and a winter road extends from Fort McKay to the hamlet of Fort Chipewyan, located on the north shore at the west end of Lake Athabasca (FIGURE 1). From the north, an improved road extends from the town of Fort Smith, located just north of the border of Alberta and the Northwest Territories, to the locality of Peace Point, situated on the Peace River north of Lake Claire. From Peace Point southeast to Fort Chipewyan, the road is classed as a winter road. Airports or airstrips are located in Fort Smith, Northwest Territories, in Fort Chipewyan, Alberta, and in Stony Rapids and Uranium City, Saskatchewan. Aircraft can also land on the water at the locations above, as well as at Fond-du-Lac, Saskatchewan.

Lake Athabasca was originally called Athapiscow by the Cree. The surveyor Philip Tumor and his assistant, Peter Fidler, visited the lake in 1791 and named the lake Athapiscow on Tumor's 1794 map (McCormack 1988). The word describes open areas such as lakes and swamps where willows, reeds and grasses grow (Holmgren and Holmgren 1976). On Peter Pond's 1790 map and Alexander Mackenzie's 1802 map, the lake is named Lake of the Hills (McCormack 1988).

The region's fur trade began in 1778, when Peter Pond established a trading post on the Athabasca River at its junction with the Embarras River (FIGURE 2) at a location now known as Old Fort. The location was unsatisfactory and, in 1788, Alexander Mackenzie's cousin, Roderick, established a new post, Fort Chipewyan, for the North West Company. It was located on what is now Indian Reserve 201A, also called Old Fort Point, on the southwest shore of Lake Athabasca west of the Old Fort River (FIGURE 2). In 1798, Fort Chipewyan was moved to the north shore to a location about 2 km from its present site. In 1802 and 1815, two Hudson's Bay Company posts were built nearby. Rivalry between the Hudson's Bay and North West companies was intense until the two companies amalgamated in 1821. The Hudson's Bay Company then held a monopoly on trade in the area until 1870, when it sold its holdings to the new Dominion of Canada (McCormack 1988).

Fort Chipewyan is Alberta's oldest permanent settlement, and in 1988, residents celebrated the bicentennial of its establishment. After the explorers and fur traders, missionaries were among the next white people to arrive at the fort. In 1849, Oblate priests established the Nativity of the Blessed Virgin Mission, and in 1874, the Grey Nuns opened Holy Angels Convent, a residential school and orphanage. In 1897, hundreds of prospectors travelled to the Klondike gold fields through Fort Chipewyan, using the traditional fur trade route down the Athabasca River. This influx of travellers led to the establishment of a North West Mounted Police Post at the fort in 1898 (McCormack 1988).

Beaver, Chipewyan and Cree Indians have inhabited the Athabasca region for the past 2,000 years or more. By the midnineteenth century, the Beaver had moved from the west end of Lake Athabasca and settled farther west, in the Fort Vermilion region. The Chipewyan and Cree then became the two dominant groups trading furs at Fort Chipewyan (McCormack 1988). In 1899, the Canadian government negotiated land cessions with the local Indians and Métis. Chipewyan Indian Reserves 201 and 201A to 201E were assigned. They are located on the delta between Lake Athabasca and Richardson Lake (FIGURE 2). Few people live on the reserves; most natives live in Fort Chipewyan, which had a population of 1,767 people in 1986 (Alta. Native Aff. 1986). In 1987, the Cree band signed an agreement with the federal and Alberta governments that will establish a Cree reserve (McCormack 1988).

For many years, the Athabasca-Slave River system served as a major transportation route. Canoes were the original mode of travel for native people and, subsequently, the fur trade. By 1822, Chipewyan boats, which were similar to York boats, were used on Lake Athabasca and later, steamers plied the waters. By 1937, the Northern Transportation Company operated the first all-steel ships on the Athabasca-Mackenzie River system from the head of navigation in the Fort McMurray area (Brady 1983). Air transport and the opening of the Mackenzie Highway in the 1950s brought competition for cargo transport. Competition increased in 1965, when the railway opened from northern Alberta to Pine Point in the Northwest Territories, and water transport to Pine Point and Hay River via the Athabasca-Slave system was reduced to a trickle (PADPG 1972). In the early 1980s, the mines near Uranium City shut down, reducing the need for barge transport across Lake Athabasca. In 1982, the Northern Transportation Company discontinued its barge service, but some commercial barge service still operates between the Fort McMurray area and Fort Chipewyan. As recently as 1983, a passenger boat service also operated between these two centres (Brady 1983).

Lake Athabasca does not have a high potential for recreation in comparison to surrounding lakes. The transparency of the water in the main part of the lake is high and algal concentrations are low, but the lake is generally too cold for swimming or water skiing and is often subject to high waves, which are dangerous for pleasure boating (PADPG 1972). There are no provincial boating regulations specific to the lake, but federal regulations apply (Alta. For. Ld. Wild. 1988). Species of sport fish in Lake Athabasca include lake trout, Arctic grayling, lake whitefish, goldeye, northern pike, yellow perch and walleye. There are no sport fishing regulations specific to the lake, but provincial limits and regulations are in effect (Alta. For. Ld. Wild. 1989). Lake Athabasca supports a domestic fishery and a commercial fishery for lake trout, lake whitefish, walleye and northern pike.

There are five recreational facilities on or near the Alberta end of the lake (FIGURE 2). Three of them are operated by the Alberta Forest Service. The first facility, Dore Lake Forest Recreation Area, is located 17 km northeast of Fort Chipewyan and about 1.5 km northwest of the shore of Lake Athabasca. It is open from May to September and has ten campsites, pump water, and a day-use area with picnic tables, a beach and a change house. The second and third facilities, Bustard Island and Richardson River Forest Recreation areas, are both boat-in sites that have several random campsites and no services. Fort Chipewyan provides services such as a boat launch, grocery stores, restaurants, hotels, lodges and a gas station.

Wood Buffalo National Park is the fourth recreation area. It was established in 1922 to protect one of the few remaining herds of wood bison and several herds of plains bison (PADPG 1972). It is the second largest national park in the world, and supports the world's largest herd of free-roaming bison. In 1985, it was designated a World Heritage Site. The park includes approximately 80% of the Peace-Athabasca Delta; it is maintained in its natural state and only limited management is permitted (PADIC 1987).

The fifth facility, the Athabasca Dunes Ecological Reserve, is located 160 km north of Fort McMurray and 26 km east of Wood Buffalo National Park (FIGURE 2). It is a vast wilderness area where active sand dunes are constantly changing the landscape and stable dunes lie under a cover of grasses. Rare plants grow in the reserve, and its many lakes and wetland areas support waterfowl populations during migration. Ecological reserves are maintained in their natural state and are used for nature appreciation, photography and wildlife viewing (Alta. Rec. Parks n.d.).

Drainage Basin Characteristics

Lake Athabasca drains an enormous area of land (282,000 km2 , TABLE 1) that extends southwest across the width of Alberta to the Columbia Icefield in the Rocky Mountains, and east across most of northern Saskatchewan to Wollaston Lake (FIGURE 1). The Peace-Athabasca Delta, which is one of the world's largest freshwater deltas, plays an important role in Lake Athabasca's complex drainage system. The delta region consists of three smaller deltas: the Athabasca (1,960 km2), the Peace (1,680 km2) and the Birch (168 km2). Its major lakes-Claire, Baril, Mamawi and Richardson-are all very shallow (PADPG 1973). River channels that meander across the delta join the major lakes to Lake Athabasca and drain upland areas.

The mean annual inflow to Lake Athabasca and the delta system is estimated to be 45,900 x 106 m3 of water (TABLE 1). A major portion of the inflow enters the lake and delta during the period from April to mid-July. The largest portion of the total inflow (53%) reaches the lake and delta system via the Athabasca River and its tributaries (FIGURE 1). The river enters Lake Athabasca through a system of channels that cut through the Athabasca Delta: the Embarras River, Fletcher Channel, Goose Island Channel and Big Point Channel (FIGURE 2). Because the Athabasca River flows into Lake Athabasca near the outlet, water from the river tends to flow through the west end of the lake quite directly, without substantial mixing with water in the main part of the lake. Inflowing water from the river usually is restricted to an area that reaches about 8 km offshore of the delta. During periods of high inflow combined with strong westerly winds, however, Athabasca River water can flow east as far as Bustard Island (Neill et al. 1981), and has been reported to extend well into Saskatchewan (Rawson 1947[a]).

Lake Athabasca's second largest water source is the Fond du Lac River, which provides approximately 21 % of the total inflow to the lake and delta region (Neil) et al. 1981). This river drains Wollaston Lake, Saskatchewan and a large area of Precambrian Shield in the eastern part of the drainage basin (FIGURE 1). Wollaston Lake has two outlets; about 10% of its outflow enters the Fond du Lac River and the remainder discharges into the Cochrane River (MRBC 1981). The Fond du Lac River flows into Fond du Lac and then into the narrow eastern end of Lake Athabasca (FIGURE 2). Along the north and south shores, dozens of other streams flow into the lake. Inflows to the south side of the lake and delta, such as the Richardson, Maybelle, Old Fort, William and McFarlane rivers, provide less than 6% of the total inflow, and the Birch River system, which flows through lakes Claire and Mamawi into the western side of Lake Athabasca, provides less than 3%. Part of the time, flow from the Birch River system bypasses Lake Athabasca and flows north to the Peace River. Miscellaneous inflows and direct runoff from the catchment area provide the final 18% of the total inflow (Neill and Evans 1979).

Lake Athabasca is drained by Rivière des Rochers and its distributary, Revillon Coupé, which carry most of the outflow. Smaller volumes flow from the lake through Chenal des Quatre Fourches (FIGURE 2). These three rivers join the Peace River to form the Slave River. Mamawi Lake, to the west of Lake Athabasca, is also drained by Chenal des Quatre Fourches. The volume of water leaving Lake Athabasca via Rivière des Rochers, Revillon Coupé and Chenal des Quatre Fourches is partly dependent on the water level in the Peace River. The predominant direction of streamflow in the three channels is northward, toward the Peace River (FIGURE 1, inset). During spring or summer flooding, however, flow reversals in the channels can occur when the elevation of the Peace River exceeds the elevation of Lake Athabasca. This results in reversed flows in Rivière des Rochers, Revillon Coupé and Chenal des Quatre Fourches. As well, flow reversals can occur between Lake Athabasca and the delta lakes. At these times, strong easterly winds cause water from Lake Athabasca to flow west into the southwestern arm of Chenal des Quatre Fourches and then into the delta lakes rather than north into the Peace River (PADIC 1987). When inflow from the Athabasca River to Lake Athabasca is high during spring and summer, an estimated 80% to 90% of the lake's outflowing water originates from the Athabasca River (Neill et al. 1981). During fall and winter, more of the outflow originates from the main body of the lake.

The drainage network of the delta is made up of open drainage and perched basins. The open drainage network is an interconnected system of lakes and streams. Its extent is related to water levels in the delta. Perched basins, which have surface levels higher than the surrounding water table, are located between the open-water drainages. They are separated from groundwater by impermeable beds, so their existence depends on flooding. The topography of the delta is quite flat, so minor changes in water levels can cause either extensive flooding or drought (PADIC 1987): In the mid-1960s, the Government of British Columbia created Williston Lake by constructing the W.A.C. Bennett Dam on the Peace River. The resulting low water levels downstream threatened the ecological balance in the Peace-Athabasca Delta when annual floods did not occur. In 1971, the governments of Canada, Alberta and Saskatchewan established the Peace-Athabasca Delta Project Group to evaluate methods of raising water levels in Lake Athabasca and the delta lakes (PADPG 1973). In the fall of 1971, a temporary rockfill dam was constructed on the southwestern arm of the Chenal des Quatre Fourches, near Mamawi Lake. On recommendation of the Peace-Athabasca Delta Project Group, the three governments signed the Peace-Athabasca Delta Implementation Agreement. The agreement gave high priority to conservation of the Peace-Athabasca Delta and the governments agreed to jointly construct control structures on Rivière des Rochers and Revillon Coupé.

In 1974, the temporary control structure on Chenal des Quatre Fourches was severely damaged by flooding. It was removed in 1975, and during 1975 and 1976, permanent control structures were built on Revillon Coupé and Rivière des Rochers (PADIC 1987). In order to allow movement of boats past the weir on Rivière des Rochers, a tramway was built in 1976 and upgraded in 1986. The tramway operates during the open-water season and is maintained by Alberta Environment. The success of the two weirs in restoring water levels in the delta and the effect of the weirs on the delta's biological community were evaluated during 1983 and 1984 by the Peace-Athabasca Delta Implementation Committee (1987). It was concluded that, although the weirs did not reproduce natural condi­tions, they had nearly restored peak summer water levels in the delta and had successfully counteracted many of the hydrological changes in the delta caused by regulation of the Peace River by the Bennett Dam. The weirs did not affect water levels in the Peace River, so the perched basins that relied on flooding from the Peace River were lost.

The Alberta portion of Lake Athabasca's drainage basin covers a range of ecoregions. In the Rocky Mountains, where the headwaters of the Athabasca River are located (FIGURE 1), the watershed is part of the Alpine, Subalpine and Montane ecoregions. The dominant vegetation consists of heath (Phyllodoce spp.) in the Alpine Ecoregion, lodgepole pine with secondary succession by Engelmann spruce in the Subalpine Ecoregion and Douglas fir in the Montane Ecoregion. North and south of Hinton lie the Boreal Uplands. Lodgepole pine is the dominant tree, with secondary succession by white and black spruce. The area surrounding Hinton and Edson is part of the Boreal Foothills, where trembling aspen, balsam polar and lodgepole pine are the main trees and secondary succession is by white and black spruce. The watershed from Whitecourt northeast to the PeaceAthabasca Delta and the southern shore of Lake Athabasca is mainly Boreal Mixedwood. Trembling aspen and balsam poplar are the major tree species. North of the lake lies the Boreal Northlands, where trembling aspen and white spruce are the dominant trees (Strong and Leggat 1981). The area of open woodland that covers the northeast section of the drainage basin (FIGURE 1) is characterized by scattered spruce and tamarack with a lichen understory. South of this area, throughout the Saskatchewan side of the drainage basin, the land is covered by Boreal Forest composed of jack pine and black spruce interspersed with many barren patches (Natl. Atlas Can. 1974).

Except for mountainous areas, soils in the southwest portion of the watershed are mainly Gray Luvisols. Northwest of Lesser Slave Lake, there are large areas of predominantly Gray Luvisols or Organic Fibrisols. In the Peace-Athabasca Delta, Cumulic Regosols are the main soil group, and in the area south of the delta and along the southern shore of Lake Athabasca the soils are mostly Humo-ferric Podzols. The area immediately north of the lake is mainly rockland, and soils in the remainder of the Saskatchewan portion of the drainage basin are excessively stony Humo-ferric Podzols with rock outcroppings (Natl. Atlas Can. 1974).

Generally, most of the drainage basin is covered by forest, bush and wetlands (FIGURE 1). Major agricultural areas are located in the southwestern part of the watershed: near Lesser Slave Lake and the town of Edson, along the Paddle and Pembina rivers, around the town of Athabasca, and south of Lac La Biche. Large areas of Precambrian Shield are located north of Lake Athabasca and the Fond du Lac River.

Forestry is a major industry throughout the Alberta side of the drainage basin. In 1988, there were pulp mills operating near the towns of Whitecourt and Hinton, and another pulp mill was scheduled to open in the summer of 1990 near Whitecourt. A pulp mill was also approved on the Lesser Slave River near the town of Slave Lake in August 1989.

The extraction of nonrenewable resources from the drainage area is economically important as well. Minerals present in the Lake Athabasca region include gypsum, granite, gold and uranium. Mining in the region began in the 1930s and was concentrated in the Saskatchewan portion of the drainage basin (PADPG 1972). Uranium is mined at Cluff Lake, Wollaston Lake and at the headwaters of the Geikie River, all in Saskatchewan (Natl. Atlas Can. 1974; Noton 1989). Coal is extracted at several mines in the Hinton area of Alberta and there are two oil sands mining and upgrading plants north of Fort McMurray (Noton 1989).

For the most part, the drainage basin is sparsely populated. The only city is Fort McMurray, and the highest concentration of towns and small communities is in the southwest portion of the watershed. Near Lake Athabasca, the only urban centres are Fort Chipewyan in Alberta, and Uranium City, Eldorado, Camsell Portage, Fond-du-Lac and Stony Rapids in Saskatchewan.

Lake Basin Characteristics

Lake Athabasca covers an area of approximately 7,770 km2 (TABLE 2). A bathymetric map is not available, but soundings have been made for navigation routes (FIGURE 2). The lake is shallowest on the Alberta side, where the maximum depth is 16 m. The shallow depths and gradual slope of the lake bottom at the western end probably result from sedimentation of the Athabasca River inflow. The central portion of the lake, between Camsell Portage on the north shore and the William River inlet, is the deepest part, with a maximum depth of 124 m near Easter Headland. East of Crackingstone Peninsula, the lake becomes shallower again, with a maximum depth of about 46 m. Lake Athabasca becomes increasingly narrow at its eastern end; soundings east of Fond-du-Lac indicated depths of 29 to 50 m in the centre of the narrow basin. There are dozens of islands throughout the lake. The islands that extend from Fort Chipewyan to the Old Fort River were formed as a result of wave action (MRBC 1981).

The north and south shores of Lake Athabasca are strikingly different. To the north lies rough, rocky Precambrian Shield, whereas to the south lies an extensive area of sand dunes (MRBC 1981). The dunes formed after proglacial lakes drained, when newly exposed sediments were subjected to intense wind storms (Bayrock and Root 1973). This activity formed dunes along the Athabasca River, in the lowlands west of Lake Claire and along the south shore of Lake Athabasca. As well, the William, McFarlane and Archibald rivers deposit large amounts of sand at their mouths, contributing to the beaches along the south shore of the lake.

The elevation of Lake Athabasca has been monitored at Fort Chipewyan for various periods since 1930, at Goldfields from 1942 to 1956, and at Crackingstone Point (on the western tip of Cracking­stone Peninsula) since 1956. The water level at the west end of the lake fluctuates because of wind action. During windy periods, water levels at Fort Chipewyan and Crackingstone Point may differ by as much as 1 m for a period of several days (PADIC 1987). Water Survey of Canada reviewed and co-ordinated the records from the three stations for the period from 1930 to 1972 (Bennett and Card 1972). This compilation is presented in Figure 3, along with lake level data recorded at Fort Chipewyan for the period from 1973 to 1987. Over the period of record, the lake level has fluctuated 5.53 m, from a maximum elevation of 211.33 m, recorded in July 1935, to a minimum elevation of 205.80 m, recorded in February 1970. The low levels observed during the period from 1968 to 1971 were due to the filling of Williston Lake on the Peace River. After the temporary control structure was built on Chenal des Quatre Fourches in the fall of 1971, the levels of lakes Athabasca (FIGURE 3), Claire and Mamawi increased. Since the permanent control structures on Revillon Coupé and Rivière des Rochers were completed in 1976, the amplitude of annual water level fluctuations in Lake Athabasca appears to be smaller than under natural conditions.

Water levels recorded before and after construction of the weirs do not provide a valid measurement of the effectiveness of the weirs because low precipitation levels during the late 1970s and the 1980s resulted in reduced runoff from the drainage basin. Therefore, a simulation of Lake Athabasca water levels for the period from 1960 to 1984 was conducted to evaluate the effect of the control structures (PADIC 1987). The report concluded that average summer maximum lake levels, simulated with the weirs in place, matched the simulated natural levels (without Bennett Dam or weirs) within 0.1 m. Simulated minimum annual water levels with weirs in place, however, were higher than simulated natural levels by 0.6 m and simulated mean annual levels were higher by 0.4 m. The mean amplitude of annual levels with the weirs in place is about 0.6 m smaller than under natural conditions.

Water Quality

Researchers from the University of Saskatchewan studied the water quality in Lake Athabasca during the late 1940s (Rawson 1947[a]; 1960). More recently, Alberta Environment occasionally sampled water quality from several sites on the Alberta section of the lake in 1979, 1980, 1987 and 1988 (Alta. Envir. n.d.[a]; Neill et al. 1981).

Samples were taken in the main part of the lake at two stations between Burntwood Island and the Alberta/Saskatchewan border in July 1987 and August 1988. These samples indicated that the water was fresh and not very turbid (TABLE 3). Total hardness and alkalinity values were low for an Alberta lake outside of the mountains. Samples were also taken at the west end of the lake near Fort Chipewyan and offshore of the Peace-Athabasca Delta during the open-water season in 1987. These sites are influenced by inflow from the Athabasca River. This is particularly evident at the delta site, where the water is well-buffered and turbid and the concentrations of most ions are much higher than at the other three sites. As in the late 1940s study, the main ions at all sites in 1987 and 1988 were bicarbonate and calcium.

There is a strong contrast between the specific conductance of Athabasca River water, with a value of 400 µS/cm, and water in the main part of the lake, with a value of about 85 µS/cm. At the lake's outlet, Rivière des Rochers, the two types of water sometimes stratify and form a distinct conductivity gradient from the surface to the bottom of the water column that is not present in the main part of the lake (FIGURE 4). In March 1980, conductivity values in the outlet ranged from about 110 µS/cm at the surface to 233 µS/cm near the bottom, whereas in March 1988 near the provincial border, specific conductivity throughout the water column was more uniform, ranging from 93 µS/cm at the surface to 81 µS/cm at the bottom.

In July 1987 and August 1988, the water column was thermally stratified at the two sampling stations in the main part of the lake (FIGURE 5). The temperature gradient was more pronounced at the deeper site (13 m) near the provincial border. The highest surface temperature recorded at the two stations was 17.4°C at the Burnt­wood Island site in July 1987. Samples were also taken at the two shallower sites, offshore of the delta (2 to 4 m) and near Fort Chipewyan (6 to 8 m). At these two stations the water column was isothermal throughout the open-water season in 1987. The highest surface temperature recorded was 18.9°C near the delta in August 1987.

Dissolved oxygen concentrations were uniform or nearly uniform from surface to bottom at the two stations between Burntwood Island and the border in July 1987 and August 1988 (FIGURE 5). During winter, the water column was well oxygenated at these sites. In March 1988, the concentration of dissolved oxygen at a depth of 1 m was 14 to 15 mg/L, and in water near the sediments, the concentration declined only slightly, to 10 to 12 mg/L. At the delta and Fort Chipewyan stations, dissolved oxygen concentrations were uniformly high throughout the water column during the open-water period in 1987 and under ice in March 1988.

It is not possible to properly categorize the trophic status of Lake Athabasca because the lake has not been sampled sufficiently. Low concentrations of total phosphorus (9 to 14 mg/L) and moderately high Secchi transparencies (3.8 to 4.8 m) were recorded in single samples from the main part of the Alberta side of the lake in July 1987 and August 1988 (TABLE 4). In combination with the low chlorophyll a concentration (1.1 µg/L) recorded on both dates, these data indicate that the main part of the lake is quite unproductive, possibly oligotrophic. Near Fort Chipewyan and the delta, however, the lake is more productive. At the delta station, where the influence of Athabasca River water is great, the maximum chlorophyll a concentration recorded during the open-water season in 1987 was 7.7 µg/L in mid-June. Near Fort Chipewyan during the same period, the highest chlorophyll a concentration was 3.9 µg/L, recorded in mid-May. Average iron concentrations at these two sites are extremely high because of the high concentrations of total suspended solids in the water column. The high turbidity (TABLE 3) also results in very low Secchi depths (TABLE 4).

Biological Characteristics

Plants

The phytoplankton and aquatic macrophyte communities in Lake Athabasca have not been studied. The marsh habitat of the Peace-Athabasca Delta was studied by the Canadian Wildlife Service in the late 1960s to examine the effects of regulation of the Peace River by the Bennett Dam on the flooding cycle, plants and animals of the delta (PADPG 1972; 1973). Low water levels in the delta resulted in the exposure of large areas of mud flats that quickly became colonized by spike rush (Eleocharis acicularis and E. palustris), Slough grass (Beckmannia syzigachne), common great bulrush (Scirpus validus), smartweed (Polygonum sp.), sedges (Carex spp.), reed grass (Phragmites communis) and willows (Salix spp.).

Since construction of the Rivihre des Rochers weir in 1975 and the Revillon Coupi weir in 1976, water levels in the delta, although higher than during the period from 1968 to 1971, have continued to be relatively low. The low water levels are caused by low precipitation levels that result in reduced runoff from contributory river basins. It is expected that, if runoff increases, vegetation in the parts of the delta affected by the weirs will return to their "natural" condition as it was prior to construction of the Bennett Dam. Perched basins along the Peace River, which are not affected by the weirs, will flood only rarely, and vegetation succession will accelerate toward willow/shrub communities (PADIC 1987).

Invertebrates

The Peace-Athabasca Delta and Lake Athabasca are very different environments, yet they are closely related because the delta and its associated channels and lakes are important spawning and nursery areas for Lake Athabasca fish. Comprehensive surveys of the delta region and Lake Athabasca have not been carried out. In the 1940s, researchers from the University of Saskatchewan examined the zooplankton at 18 stations in the lake but did not examine the species composition (Rawson 1947[a]). As well, 214 bottom samples were taken with an Ekman dredge, primarily in the profundal zone (Larkin 1947). The amphipod Pontoporeia affinis was the dominant benthic organism collected and the opossum shrimp Mysis relicta was rare. Even in water 0- to 5-m deep, Pontoporeia formed as much as 45% of the benthic biomass.

The zooplankton and benthic fauna of the delta were investigated by researchers from the University of Alberta in 1971 (Gallup et al. 1971). The zooplankton was sampled by single horizontal tows at various locations in the delta and was also collected from two sites in the main part of Lake Athabasca. In the lake, the most abundant cladocerans were Daphnia pulex and Bosmina longirostris and the most abundant copepods were Epischura nevadensis, unidentified Diaptomus copepodites and unidentified Cyclops copepodites. In the lakes and channels of the delta, large daphnids (Daphnia, D. magna and D. retrocurva) were quite abundant, as was the copepod Epischura nevadensis. Diacyclops bicuspidatus thomasi, which is the intermediate host for the tapeworm Triaenophorus crassus, was only locally abundant in the delta. It is likely, however, to be abundant in Lake Athabasca as well, since many lake whitefish and cisco in the lake are infected by T. crassus cysts.

In 1971, two replicate samples of bottom sediments were taken with an Ekman dredge at each of a number of locations in the delta and at two locations in Lake Athabasca. Sample depths were not given. The standing stock of benthic invertebrates in many areas of the delta seemed to be low, largely because many areas freeze to the bottom. Fingernail clams (Sphaeriidae: Sphaerium and Pisidium), midge larvae (Chironomidae) and snails (Gastropoda: Lymnaea, Physa and Promonetus) were collected at almost every station.

Fish

The fish community in Lake Athabasca includes lake trout, lake whitefish, round whitefish, cisco, shortjaw cisco, Arctic grayling, longnose sucker, white sucker, lake chub, flathead chub, emerald shiner, spottail shiner, goldeye, northern pike, ninespine stickleback, trout-perch, yellow perch, walleye, spoonhead sculpin, deepwater sculpin and burbot (Rawson 1947[b]). The Peace-Athabasca Delta is a critical spawning and nursery area for sport and commercial species found in the lake. Walleye tagged in Richardson Lake have been recovered 119 to 138 km away in Lake Athabasca after 94 to 102 days (Bidgood 1961).

Lake Athabasca supports commercial, domestic and sport fisheries. The size of the sport fish harvest is unknown, but is likely to be small because access to the lake is limited and the water often becomes too rough for small boats. The domestic harvest is also unknown, but in 1945, the annual domestic harvest was about 227,000 kg (Rawson 1947[a]). Commercial fishing began in 1926 and the catch has been recorded from 1926 to the present (Alta. For. Ld. Wild. n.d.; Sask. Parks Rec. Cult. n.d.; Rawson 1947[a]; Alta. Rec. Parks Wild. 1976).

From 1926 to 1943, most commercial fishing took place on the Saskatchewan portion of the lake. The main catches were lake trout and lake whitefish. Over this period, the total catch fluctuated widely, from a minimum of about 101,000 kg in 1932/33 to a maximum of 1,157,270 kg in 1929/30 (FIGURE 6). After one fish company stopped operating in 1929, the catch dropped to about 63,000 kg/year in 1931/32 and then continued dropping during the "depression". From 1936 to 1942, the average catch was about 318,000 kg/year.

In 1943, the Alberta fishery near the Peace-Athabasca Delta opened; northern pike and walleye were the principal species caught. In the first two years after the delta fishery began, the average harvest of all species from the whole lake was 625,000 kg/year. The records from 1945/46 to 1950/51 are incomplete, but from 1951/52 to 1959/60, the average total catch was 550,833 kg/year. The catch increased to 747,796 kg/year from 1960/61 to 1965/66. In 1966/67, the lake trout quota was reduced to prevent overexploitation and the average total catch from that year until 1973/74 was 562,114 kg/year. From 1974/75 to 1984/85 the fishery was unstable because of reduced effort, difficulties with processing plant equipment, and limitations imposed by resident fishermen on the issue of licences to nonresidents who traditionally fished for walleye and whitefish. During this period, the total harvest varied between 12,399 and 308,689 kg/year. Before the unstable period, the catch in Saskatchewan waters had been substantially greater than the harvest near the delta. From 1985/86 to 1987/88, however, the Saskatchewan fishery was based only on the south shore and the catch from Alberta was almost twice that from Saskatchewan. The average total catch from 1985/86 to 1987/88 was 377,108 kg/year.

Before the delta fishery opened in 1943/44, lake trout were the primary commercial species in Lake Athabasca. The largest catch of lake trout (1,012,409 kg) was taken in 1929/30. From 1935/36 to 1942/43, the average catch declined to only 258,000 kg/year, representing 81% of the total annual catch. From 1951/52 to 1959/60, the average catch of lake trout rose slightly, to 266,247 kg/year, but represented only 48% of the total catch. This drop in the proportion of lake trout occurred after the opening of the Alberta fishery, which caught other species. From 1960/61 to 1965/66, the average lake trout catch rose again, to 287,000 kg/year, and represented 38% of the total catch. In the early 1960s, a lake trout reported to weigh 47.6 kg was taken in a commercial net in Lake Athabasca (Larkin 1964). In 1966/67, the lake trout quota was greatly reduced, and from 1967/68 to 1973/74 the average catch declined to 110,155 kg/year, or 20% of the total catch. The harvest from 1985/86 to 1987/88 averaged 85,000 kg/year, or 23% of the total catch.

The average whitefish harvest from 1935/36 to 1942/43 was 58,000 kg/year (18% of the total catch). Following development of the delta fishery, the average whitefish catch increased. From 1951/52 to 1959/60 it was 225,375 kg/year (41% of the total catch) and from 1960/61 to 1965/66, it increased again, to 310,112 kg/year (42% of the total catch). From 1967/68 to 1973/74 the catch fell slightly, to 300,639 kg/year (54% of the total catch). Following the problems of the late 1970s and early 1980s, the whitefish harvest declined sharply-from 1985/86 to 1987/88, it was only 63,349 kg/year (17% of the total catch). Lake whitefish from the Alberta side of Lake Athabasca are infested with cysts of the tapeworm Triaenophorus crassus. Although fit for human consumption, these whitefish are considered poor quality and are used in commercial products such as fish cakes.

The walleye harvest from 1935/36 to 1942/43 was quite small, only 3,724 kg/year (1% of the total catch). After development of the delta fishery, the harvest increased. From 1951/52 to 1959/60 it was 46,500 kg/year (8% of the total catch) and from 1960/61 to 1965/66, it almost doubled, to 85,400 kg/year (11% of the total catch). From 1967/68 to 1973/74, the walleye harvest declined to 74,000 kg/year (13% of the total catch) and then remained at that level (75,000 kg/year, or 20% of the total catch) for the period from 1985/86 to 1987/88. Almost all walleye are caught in Alberta waters.

The average harvest of northern pike from 1935/36 to 1942/43 was 3,343 kg/year (1% of the total catch). It increased only slightly after development of the delta fishery. From 1951/52 to 1959/60 the harvest was 12,748 kg/year (2% of the total catch), but from 1960/61 to 1973/74, it increased to 65,730 kg/year (10% of the total catch). The average catch from 1985/86 to 1987/88 was 153,600 kg/year (41% of the total catch). Virtually all of the pike are caught in the delta region of the lake.

Wildlife

The Peace-Athabasca Delta region is the part of Lake Athabasca that is most important to wildlife. The delta is one of North America's last relatively undisturbed deltas and is unique because it is situated on all four of the continent's major flyways. Furthermore, the delta is an important breeding, staging and moulting area for waterfowl and is a nesting area for the endangered Peregrine Falcon. It supports the largest area of undisturbed sedge and grass meadows in North America and provides grazing for most of the bison of Wood Buffalo National Park (PADPG 1972). The portion of the delta lying outside Wood Buffalo National Park, with the exception of the Chipewyan Indian Reserves, was proposed as a Wildlife Habitat Management Area by Ducks Unlimited (Canada) and Fish and Wildlife Division in 1986 (Ducks Unltd. (Can.) and Alta. En. Nat. Resour. 1986). The area includes Richardson Lake, which is at present a bird sanctuary.

The effects of changes in the flow of the Peace River on the wildlife and fisheries of the delta after construction of the Bennett Dam were studied by the Peace-Athabasca Delta Project Group (1972; 1973), which was set up by the governments of Canada, Alberta and Saskatchewan. As well, during the 1980s, the effects of the Rivihre des Rochers and Revillon Coupiweirs were studied by the Peace-Athabasca Delta Implementation Committee (1987).

More than 200 species of birds have been identified in Wood Buffalo National Park, which includes a large part of the delta region. The delta is a vital stopover for Whooping Cranes, Whistling Swans, Snow, White-fronted, Ross's and Canada geese and a variety of ducks during spring and fall migration. During the spring migration of 1971, about 400,000 ducks, numerous swans, and 145,000 geese used the delta region. As well, 14 species of ducks nest and moult in the delta marshes. In 1971, the ducks that remained after migration produced about 600,000 young. About 500,000 waterfowl used the delta for moulting, and about 1,200,000 ducks and 165,000 geese and swans stopped and fed in the large lakes of the delta during the fall migration that year (PADPG 1972). Other important bird species that inhabit the region include Sandhill Crane, Ring-billed Gull, Common Tern, Greater Yellowlegs, Wilson's Phalarope, Franklin's Gull, Eared Grebe, Western Grebe, Long-billed Marsh Wren, Yellow-headed Blackbird, Osprey, Bald Eagle and Peregrine Falcon (Can. Wild. Serv. 1985; Ducks Unltd. (Can.) and Alfa. En. Nat. Resour. 1986).

Statistical analyses of waterfowl populations with data from 1960 to 1980 indicated no significant differences among waterfowl populations for the pre-Bennett dam, post-Bennett dam and postweir periods. A simulation model predicted that long-term production after the weirs were built would approximate production under natural conditions. The available habitat for fall staging, however, would decrease from the amount present under natural conditions because the weirs cause autumn water levels to decline more slowly (PADIC 1987).

The delta region and Wood Buffalo National Park provide important habitat for mammals. Altogether, 45 species of mammals have been recorded in the park (PADPG 1972). Muskrat populations in the delta were estimated to be between 200,000 and 2,000,000 animals prior to construction of the Bennett Dam. Muskrats thrive in the deeper perched basins provided these basins are refilled by floods every four or five years (Can. Wild. Serv. 1985). Muskrat trapping and, to a lesser extent, beaver and mink trapping, are important sources of income to natives in the delta region. In 1974, muskrat numbers peaked in response to higher water levels, which were caused by precipitation levels that were higher than those in previous years. Since 1975, however, muskrat numbers have declined. This decline may have been influenced by trapping, predation and disease, as well as by declining water levels. If overall water levels in the delta increase-for instance, during periods of greater precipitation-the habitat necessary for the muskrat population to recover will be present. Along the Peace River, where less frequent flooding of perched basins since the Bennett Dam was built has not been influenced by the weirs, a long-term decline in the muskrat population is expected (PADIC 1987).

In 1971, about 10,000 of the 14,000 bison in Wood Buffalo National Park fed in the delta year-round (PADPG 1972). The bison calve and raise their young on the Sweetgrass Meadows north of Lake Claire, then move toward Mamawi Lake in the fall. By midwinter they are dispersed over small sedge meadows near the lake, and in spring they drift back to the Sweetgrass Meadows (Can. Wild. Serv. 1985). Moose inhabit the higher, forested areas of the delta, and in 1971, an estimated 800 moose lived in the area. Timber wolves are the dominant carnivore in the delta and black bears are present as well.

M.E. Bradford and J.M. Hanson

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