Question

Why does fertilizer runoff into a body of water such as a lake or ocean (eutrophication) often result in water with too little oxygen for fish to live?

Answer 1

Eutrophication

Eutrophication is the process by which a body of water such as lake and ocean becomes enriched in dissolved nutrients nitrogen or phosphorus or the oversupply of nutrients occurs.

These oversupply of nutrients stimulate the growth of aquatic plant life usually resulting in the depletion of dissolved oxygen.

Generally aquatic plants occupy surface of water make unable to penetrate even sunlight into the water.

Oxygen dissolves in surface of water by aerating action of winds. Here the excess growth of plant interfere aeration process. Results in reduce oxygen concentration.

So dissolved oxygen concentration becomes too low as result fish and other aquatic organisms cannot survive.