eutrophic

[adjective]

A water body where the nutrient content (particularly phosphorus) is so high that quickly reproducing plants, like algae, form a thick mat on the surface of the water. This mat prevents sunlight from penetrating the water, which in turn prevents other aquatic plants from photosynthesizing. Over time, the amount of dissolved oxygen in the water decreases and aquatic animals suffocate. A eutrophic water body is one where this process has been underway for some time.