Heated waste water is commonly disposed of by draining it into lakes, streams, and oceans. Why is it a problem

Answer 1

Warm water cannot hold as much gas as cold water. It also increases algae growth in many shallow lakes. In northern latitudes algae will absorb more oxygen then it will produce once again dropping the oxygen level. Then on the fish side, warmer temperature causes the fishes metabolism to speed up. They require more oxygen and food. The oxygen level is already lowered by the other two levels and food is usually not very abundant for most fish in these areas. So basically the life in the lake or that area of the ocean can either suffocate or starve.

Answer 2

Warm water doesn't hold as much oxygen as cool water, so the fish and other heterotrophs suffer from lack of oxygen. Since larger fish need more dissolved oxygen, larger fish have a bigger problem than smaller fish have.