Mackenzie River east into the Churchill River. The eastern portion of the Mackenzie basin is dominated by vast reaches of lake-studded boreal forest and includes many of the largest lakes in North America. By both volume and surface area, Great Bear Lake is the biggest in the watershed and third largest on the continent, with a surface area of and a volume of . Great Slave Lake is slightly smaller, with an area of and containing of water, although it is significantly deeper than Great Bear. The third major lake, Athabasca, is less than a third that size with an area of
Lake Huron as two 'lobes of the same lake'). Aggregated, Lake Huron-Michigan, at , "is technically the world's largest freshwater lake." When counted separately, Lake Superior is larger than Huron and higher. Lake Superior drains into the St. Marys River which then flows southward into Lake Huron. The water then flows south to the St. Clair River, at Port Huron, Michigan and Sarnia, Ontario. The Great Lakes Waterway continues thence to Lake St. Clair; the Detroit River and Detroit, Michigan; into Lake Erie and thence – via Lake Ontario and the St. Lawrence River – to the Atlantic Ocean. Like the other