|Lat / Long||53.4000000, -113.0666667|
|Max depth||8.5 m|
|Mean depth||4.7 m|
|Dr. Basin Area||2.43 km2|
|Drainage Basin||North Saskatchewan River Basin|
|TP x||112 µg/L|
|CHLORO x||57.0 µg/L|
|TDS x||165 mg/L|
Halfmoon Lake is a picturesque little crescent of water located just east of the city of Edmonton, in the County of Strathcona. To travel to the lake from Edmonton, drive east on the Sherwood Park Freeway and Wye Road (Secondary Road 630) until you are 3 km east of the hamlet of Sherwood Park; turn south onto Highway 21 and drive for 9.6 km, then turn east onto Secondary Road 629 and drive for 10.5 km until you reach the local road that provides access to the south side of the lake (FIGURE 1).
The lake was probably named for its crescent shape; the first documentation of the name appears on a 1915 federal government map. Little is known of the history of the lake, but it is now very popular for recreation as it is easily accessible from Edmonton for a day or evening visit. There is no public campground or day-use area at the lake, but Halfmoon Lake Resort, a commercially operated facility at the south end of the lake, is open from May to October and offers 90 campsites, washroom facilities, a developed beach, a wading pool, groceries, a boat launch and other amenities (FIGURE 2). The east and west shores of the lake are developed with 35 country residential lots. There is no Crown land around the lake.
The resort area and beach at the south end of the lake are very heavily used in summer. Popular activities at the lake are swimming, canoeing and water skiing in summer and snowmobiling in winter. There are no boating restrictions over most of the lake, but in posted areas such as the designated swimming area, all boats are prohibited (Alta. For. Ld. Wild. 1988). Algal blooms turn the lake water green from early summer until fall. Large leeches are common. When the algae decay in winter, most of the dissolved oxygen in the lake is consumed; the only fish that can overwinter are brook sticklebacks. Sport fishing is available near the lake in an aerated trout-pond stocked and operated by Halfmoon Lake Resort.
The drainage basin of Halfmoon Lake covers a small portion (2.43 km2, TABLE 1) of the Cooking Lake Moraine. It is formed of rolling glacial till; the land rises from approximately 745 m near the lake to 760 m in the low hills to the west and north of the lake. The drainage basin is small compared to the lake area (6:1) and provides little inflow - only one intermittent stream flows into the lake, at the eastern end. The outflow drains intermittently into Cooking Lake. The amount of groundwater inflow and outflow is not known.
The watershed is part of the Moist Mixedwood Subregion of the Boreal Mixedwood Ecoregion (Strong and Leggat 1981). The dominant trees are trembling aspen and balsam poplar and the soils in the area are Orthic Gray Luvisols. The arability rating of the land is poor to fair (Bowser et al. 1962), and only about one-quarter of the basin has been cleared for agriculture (FIGURE 1), mostly for pasture and mixed farming. The eastern portion of the north and south shores has been extensively developed for recreational use and for country residential properties.
Halfmoon Lake is a tiny lake with a surface area of only 0.41 km2 (TABLE 2, FIGURE 3); it has a single, elongate basin with a maximum depth of 8.5 m (FIGURE 2). Approximately 40% of the lake is less than 4-m deep (FIGURE 3). The lake bottom slopes moderately steeply at the south end and along the north and south sides, but very gradually at the west end. The residence time of water in the lake is long (60 years) based on surface inflows (TABLE 2). The lake level has not been monitored.
The water quality of Halfmoon Lake has long been a concern. Dissolved oxygen concentrations were monitored by Fish and Wildlife Division from 1955 to 1961, and again in 1967 (Alta. For. Ld. Wild. n.d.). The University of Alberta monitored water quality intensively from 1981 through 1983 (Prepas n.d.; Prepas and Trew 1983; Riley 1983; Babin 1984; Riley and Prepas 1984; Babin and Prepas 1985) and Alberta Environment monitored the lake in 1987. In 1988 and 1989, the lake became the subject of an experimental lake restoration program and was monitored intensively by both the University of Alberta (Prepas n.d.) and Alberta Environment (Alta. Envir. n.d.[a]).
Halfmoon Lake has fresh, well-buffered water. The dominantions are bicarbonate, calcium and sodium (TABLE 3). The lake becomes thermally stratified in early summer and remains so until fall. In 1982, thermal stratification was evident by late May and continued until late September (FIGURE 4). The bottom water was anoxic by early June in 1982, and remained so until mid-October (FIGURE 5). In late fall, although the lake water was the same temperature from top to bottom, winds were light and dissolved oxygen concentrations reached only 48% saturation before freeze-up. Under ice cover, the dissolved oxygen consumption rate was very high (0.462 g O2/m2 per day), and by mid-January of 1983, the whole water column was anoxic (Babin and Prepas 1985).
Halfmoon Lake is hyper-eutrophic, and dense algal blooms are common during most of the summer. The total phosphorus concentration in the euphotic zone was high in May 1982 (TABLE 4, FIGURE 6), likely because phosphorus had been released from the bottom sediments into the anoxic water column under ice cover. Total phosphorus concentrations increase under ice: on 10 March 1983, the concentration ranged from 157 µg/L just under the ice to 344 µg/L at a depth of 7 m. Algae respond to the abundant phosphorus in the water column with a spring algal bloom - the chlorophyll a concentration reached at least 88 µg/L in 1982 (FIGURE 6). Throughout the summer, chlorophyll a concentrations closely paralleled total phosphorus concentrations in the epilimnion. After the lake became thermally stratified in June 1982, the lower strata quickly became anoxic and total phosphorus concentrations in the hypolimnion rose dramatically. By 11 June, the total phosphorus concentration at 1 m above the lake bottom was 806 µg/L, and by 20 August it had increased to 1,350 µg/L at 1 m above the bottom and 644 µg/L at 2.5 m above the bottom (Riley and Prepas 1984). When thermal stratification broke down in September 1982 and the water column mixed, an immense amount of phosphorus was transferred from the hypolimnion to the surface water, causing the total phosphorus concentration in the epilimnion to increase to 190 µg/L. Algal biomass did not respond to this phosphorus peak, possibly due to the simultaneous mixing of residual herbicides such as copper sulphate, which have been applied to Halfmoon Lake in the past. A similar situation was observed in Figure Eight Lake near Peace River: mixing in the autumn was accompanied by the resuspension of copper sulphate, which had last been applied several years previously, and algal growth was low despite the high phosphorus concentrations (Prepas et al. 1987).
In 1988, an experimental project to reduce phosphorus and chlorophyll concentrations was initiated by the County of Strathcona, Halfmoon Lake Resort, Alberta Environment and the University of Alberta. Fifty-eight tonnes of calcium carbonate (powdered limestone) and 40 tonnes of calcium hydroxide (hydrated lime) were added in July 1988, and an additional dosage of 138 tonnes of calcium hydroxide was added in August 1989. In 1989 the mean total phosphorus concentration (May to August) was 67 µg/L, maximum total phosphorus concentration was 90 µg/L. This was a lower mean total phosphorus concentration than recorded in 1982 for a similar period (107 µg/L), and a lower maximum total phosphorus concentration than recorded in any of the four previous years on record. Similarly, average chlorophyll a concentration was lower in 1989 than in 1982 (30 versus 69 µg/L), although there was a substantial algal bloom in July 1989 (maximum chlorophyll a 82 µg/L). A joint research program set up in 1989 between the University of Alberta and the Alberta Environmental Centre is expected to continue for three to five years.
Halfmoon Lake was one of 31 lakes in the area between Edmonton and the Beaver River that were sampled between mid-July and early August in 1983 (Alta. Envir. n.d.[a]). Halfmoon Lake had the highest chlorophyll a concentration (148 µg/L) and the second highest algal biomass (32.0 mg/L; second only to Lac la Nonne) of the 31 lakes. Over 97% of the algal biomass was Aphanizomenon flos-aquae.
Aquatic macrophytes grow profusely at the northwest end of the lake but there has been no documentation of the species present there.
There is no information on invertebrates in Halfmoon Lake. A study to document the invertebrate community was in its initial stages in 1988 (Alta. Envir. n.d.[a]).
Halfmoon Lake becomes completely anoxic in many winters and no fish species can survive except brook stickleback. However, the popularity of the lake and its proximity to Edmonton has led to persistent efforts by Fish and Wildlife Division to establish a sport fishery (Alta. For. Ld. Wild. n.d.). The lake was stocked with rainbow trout in 1955 and 1956, but angling success was poor in 1956 and no fish were caught by test netting in 1957. Perch were stocked in 1957 and pike in 1958, but no fish were caught by angling in 1959 or by test netting in 1960. A last attempt at stocking perch was made in 1960, but these fish also succumbed to winterkill in the first winter. In 1962, the owner of Halfmoon Lake Resort installed an aerator in the lake to try to keep winter dissolved oxygen concentrations sufficiently high to overwinter sport fish. The aerator operated continuously all winter, but by 11 March 1963, dissolved oxygen concentrations in the lake were very low (0.8 to 1.2 mg/L). In 1966, the resort owner increased the capacity of the aerator, changed the position of the hoses and started to aerate the lake just before freeze-up. However, the results were similar, and dissolved oxygen dropped to critical concentrations (1.2 to 2.0 mg/L) early in the new year. In 1967, 41,000 rainbow trout fingerlings were planted, but despite aeration, winterkill occurred once again. In 1970, 1,000 yearling northern pike and 1,000 adult yellow perch were stocked, and in 1973, an additional 450 adult pike were added. None of these fish survived the winter following their placement in the lake (Alta. For. Ld. Wild. n.d.).
The shallow weedy area at the northwest end of the lake provides good nesting habitat for waterfowl, but no details of species or densities are available.
J.M. Crosby and E.E. Prepas
Alberta Environment. n.d.[a]. Envir. Assess. Div., Envir. Qlty. Monit. Br. Unpubl. data, Edmonton.
-----. n.d.[b]. Tech. Serv. Div., Hydrol. Br. Unpubl. data, Edmonton.
Alberta Forestry, Lands and Wildlife. n.d. Fish Wild. Div. Unpubl. data, Edmonton.
-----. 1988. Boating in Alberta. Fish Wild. Div., Edmonton.
Alberta Research Council. 1972. Geological map of Alberta. Nat. Resour. Div., Alta. Geol. Surv., Edmonton.
Babin, J. 1984. Winter oxygen depletion in temperate zone lakes. MSc thesis. Univ. Alta., Edmonton.
----- and E.E. Prepas. 1985. Modelling winter oxygen depletion rates in ice-covered temperate zone lakes in Canada. Can. J. Fish. Aquat. Sci. 42:239-249.
Bowser, W.E., A.A. Kjearsgaard, T.W. Peters and R.E. Wells. 1962. Soil survey of the Edmonton sheet (83-H). Alta. Soil Surv. Rep. No. 21, Univ. Alta. Bull. No. SS-4. Univ. Alta., Edmonton.
Energy, Mines and Resources Canada. 1974. National topographic series 1:50 000 83H/6 (1974). Surv. Map. Br., Ottawa.
Environment Canada. 1982. Canadian climate normals, Vol. 7: Bright sunshine (1951-1980). Prep. by Atm. Envir. Serv. Supply Serv. Can., Ottawa.
Prepas, E.E. n.d. Univ. Alta., Dept. Zool. Unpubl. data, Edmonton.
----- and D.O. Trew. 1983. Evaluation of the phosphorus-chlorophyll relationship for lakes off the Precambrian Shield in western Canada. Can. J. Fish. Aquat. Sci. 40:27-35.
Prepas, E.E., T. Murphy and P. Manning. 1987. Report on the 1985 evaluation of Figure Eight Lake, Alberta. Prep. for Alta. Envir., Plan. Div., Edmonton.
Riley, E.T. 1983. Internal phosphorus loading from the sediments and the phosphorus-chlorophyll model in shallow lakes. MSc thesis. Univ. Alta., Edmonton.
----- and E.E. Prepas. 1984. Role of internal phosphorus loading in two shallow, productive lakes in Alberta, Canada. Can. J. Fish. Aquat. Sci. 41:845-855.
Strong, W.L. and K.R. Leggat. 1981. Ecoregions of Alberta. Alta. En. Nat. Resour., Resour. Eval. Plan. Div., Edmonton.