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 Constance St. Gallen, and Schaffhausen. The Rhine flows into the lake from the south, with its original course forming the Austro-Swiss border, and has its outflow on the "Lower Lake" where — except for Schaffhausen — it forms the German-Swiss border until the city of Basel. Lake Constance is the third largest freshwater lake in Central and Western Europe in terms of surface area (and the second largest in terms of volume), after Lake Geneva and (in terms of surface area) Lake Balaton. It is long, and at its widest point, nearly wide. It covers approximately , and is above sea