dead fish
Thousands of dead fish blanketed the Belle River near Lake St. Clair August 2014. Possible causes could be a sudden change in the water temperature during a rain storm, or sewage and bacteria in the water deprived fish of oxygen.

wildlife death

While it is normal to occasionally encounter dead wildlife, mass deaths of fish may be a sign of environmental stress, frequently as a result of a reduction in dissolved oxygen concentration in the water. Animal deaths may also occur as a result of pollution, although this tends to be less common.