The combined Peace-Athabasca Basin (including the area draining directly into Lake Athabasca) is the largest watershed in Alberta, covering 346,530 km2 or 52% of the province. The Peace and the Athabasca are two of the three largest rivers in Alberta; the Slave River, formed by their confluence, is the province's largest. On average, 110 billion m2 of water leaves Alberta via the Slave River every year, approximately 85% of the total annual volume of water flowing out of the province. This basin is also the setting for the three largest lakes in Alberta: Athabasca, Claire and Lesser Slave. The combined area covered by these three lakes is more than 3 times the combined area of all the other lakes and reservoirs discussed in the Atlas.
The Athabasca River has its headwaters on Alberta's highest mountain, Mt. Columbia, which soars to 3,750 m in Jasper National Park and is in the centre of the Columbia Icefield, the largest icefield in the Rocky Mountains. The river passes through Alpine, Subalpine and Montane ecoregions before it leaves Jasper National Park, then traverses through the diverse forest of the Boreal Foothills Ecoregion where Smoke and McLeod lakes are located. The Boreal Uplands Ecoregion lies along the foothills to the north and south of the broad Athabasca Valley; Rock Lake is one of the beautiful little lakes in this ecoregion. Before the river reaches the town of Whitecourt, it enters the Boreal Mixedwood Ecoregion and stays in it for the rest of its journey to Lake Athabasca. There are numerous lakes in this part of the Athabasca Basin, including a cluster of four small productive lakes northwest of Edmonton (Lessard, Thunder, Nakamun and Lac la Nonne), and another group north of Edmonton (Baptiste, Island, Narrow, Long (near Athabasca) and Steele). Two other lakes in the Atlas lie southeast of Fort McMurray: Gregoire, with a provincial park, and Christina, popular for its fly-in fishery for walleye and pike. The Athabasca River flows north from Fort McMurray then enters Lake Athabasca in the northeast corner of Alberta.
The Peace River starts in the Omineca Mountains in north-central British Columbia, but before it leaves that province it is impounded by the W.A.C. Bennett Dam to create Williston Lake, the largest body of fresh water in British Columbia. The Peace River flows across the Boreal Mixedwood Ecoregion for almost all of its journey across Alberta, cutting briefly into the Boreal Northlands Ecoregion in Wood Buffalo National Park. The region from the town of Peace River south into the Smoky River sub-basin is the most populated portion of the Peace River Basin and is the site of many popular lakes, including Moonshine, Figure Eight, Saskatoon, Sturgeon, Smoke, Musreau and losegun. The Peace River flows eastward across northern Alberta until it is 30 km northwest of Lake Athabasca.
However, when water levels are high on the Peace River, usually for about 20 days in early summer, the elevation of the Peace becomes higher than that of Lake Athabasca. When this happens, some of the flow in Riviere des Rochers and Chenal des Quatre Fourches reverses and water from the Peace River flows south. The high water in Riviere des Rochers and in Chenal des Quatre Fourches blocks the outflow of the Athabasca River and leads to the flooding of another outstanding feature of the Peace-Athabasca Basin: the Peace-Athabasca Delta.
The delta is an enormous area of marshes, grasslands and ponds, covering 3,775 km2. It is one of the world's most biologically productive areas and is the home of the largest free-ranging herd of buffalo in the world. The delta is of vital importance for waterfowl as a feeding and staging area on all four of the major flyways in North America. The delta was declared a World Heritage Site in 1985 and is the focus of Wood Buffalo National Park, the largest national park in the world and the only remaining nesting area for Whooping Cranes.
Other resources of the basin are also worthy of superlatives. The northern half of Alberta is much wetter than the southern half (precipitation is greater and evaporation is much less), and so trees thrive, mostly trembling aspen, and white and black spruce. Most of the Peace-Athabasca Basin is part of one of the world's largest relatively undisturbed forest areas. South of Lake Athabasca, the Athabasca River flows through the Alberta Oil Sands, a reserve of petroleum estimated to exceed all the other remaining reserves in the world.
Agriculture is the major land use in the southern portion of the basin and in the area around the town of Peace River and city of Grande Prairie. The Peace River country is the most northerly wheat-growing area in the world; the winters are cold and the growing season is short, but during the summer the day-lengths are long, up to 18 hours. Crops grow fast and the quality is excellent; some of the best-quality wheat and canola in the world comes from this region, as does most of Canada's honey. The population of the basin is concentrated in the farming areas. Approximately 150,000 people live in the Peace-Athabasca Basin, almost half of them in the area bordered by the town of Peace River, Lac La Biche and the southern edge of the Athabasca Basin.
This region not only gives rise to the largest rivers of Alberta; it is also dotted with hundreds of lakes, ponds, wetlands and muskegs. The lakes in these northern basins are numerous and varied in character. Of those discussed in the Atlas, they range in size from Lake Athabasca (7,770 km2, 124 m maximum depth) to tiny Moonshine Lake (0.3 km2, 3.5 m maximum depth). Most of them are nutrient rich and support a lush growth of rooted plants and algae; of the 23 lakes in the Atlas in this basin for which there are data, 17 are eutrophic or hyper-eutrophic.
Over half of the fish taken in Alberta's commercial fishery are taken from the Peace-Athabasca Basin. Lake whitefish constitute most of the catch, but substantial numbers of pike and walleye are also taken. The largest fisheries are on Lake Athabasca, Lesser Slave and Utikuma lakes.
The Peace and Athabasca basins are endowed with an abundance of beautiful lakes but only a few are presented in the Atlas. For many lakes the only access is by float plane, thus very little is known about them. Some of these lakes are home to isolated fishing camps, but most are still unchanged wilderness, and a visit to them is a memorable experience.