What happens when nutrient levels become too concentrated in rivers, lakes, and oceans?

Eutrophication is what happens when nutrient levels become too concentrated in rivers, lakes, and oceans.

Eutrophication is when the levels of nutrients and minerals in a body of water become too concentrated. It is usually induced by the release of nitrate or phosphate-containing substances into a water body. Eutrophication leads to an excessive growth of plants and algal which degrades water quality and it may also reduce the oxygen content of the water body. Eutrophication can cause loss of species due to reduced dissolved oxygen in the water, loss of habitat (such as destroying the lake bed habitat for invertebrate organisms) and reduced visibility and increased turbidity of water.

your answer is "the 1950's"

a "theory" a suggestion that is not 100 % accurate, or a figure. some people say its a theory because they of all the passed theory's about one subject. it depends sometimes theory might be accurate and sometimes they are.