Thanks to environmental regulation on both the US and Canadian sides of the lake, water quality has vastly improved since the 1970s.
But the lake area is still laden with heavy industry and sewage treatment plants, and the lake continues to receive large amounts of run-off from the region's agricultural areas.
Dead zones - oxygen-deprived areas where fish can't survive - still occur when excess fertilizer and untreated sewage seep into the waters.
Other eerie problems
The Great Lakes and climate change
Should climate change manage to alter the physical or chemical characteristics of the Great Lakes, an overall loss in biodiversity would result because many endemic species would be incapable of adapting to the changing conditions.
Find out from a WWF climate witness about changing climate in the Great Lakes.