Lake Superior has a maximum depth of 406 metres, making it the deepest of North America’s Great Lakes.
The deepest point lies in the lake’s eastern section, in a basin shaped largely by continental glaciation. Ice sheets excavated and widened older geological valleys during the last ice ages, leaving Superior with an exceptionally deep and rocky basin.
Lake Superior is also the largest and northernmost Great Lake. Its great depth helps moderate temperature changes, so its water remains cold even during summer. The lake’s average depth is about 147 metres, far less than its deepest point but still greater than that of the other Great Lakes.
A common mix-up is confusing maximum depth with average depth. Superior’s average depth is roughly 147 metres, while its deepest measured point reaches 406 metres below the surface.