Lake Superior other Great Lakes fish, populations have also been affected by the accidental or intentional introduction of foreign species such as the sea lamprey and Eurasian ruffe. Accidental introductions have occurred in part by the removal of natural barriers to navigation between the Great Lakes. Overfishing has also been a factor in the decline of fish populations. Lake Superior Lake Superior (; ), the largest of the Great Lakes of North America, is also the world's largest freshwater lake by surface area, and the third largest freshwater lake by volume. The lake is shared by the Canadian province of Ontario to
Lake Winnipeg algae threat the 10th largest freshwater lake in the world. The lake consists of three well-defined regions, the larger North Basin, the smaller South Basin, and the connecting body of water defined as the "Narrows", all of which are greatly affected by algae blooms. The surrounding watershed drainage basin is roughly forty times larger than the lake’s surface area, this ratio is higher than any other major lake in the world; this makes Lake Winnipeg susceptible to excessive nutrient levels. Because Lake Winnipeg holds a considerable small volume of water, the water quality is determined by manmade structures and high nutrient loading.