Excess nitrogen can cause over-stimulation of growth of aquatic plants and algae. Excessive growth of these organisms, in turn, can clog water intakes, use up dissolved oxygen as they decompose, and block light to deeper waters. So few organisms live in these conditions or even can suffocate and die.
Eutrophication is the name given to the natural nutrient enrichment of a shallow lake, estuary, or slow-moving stream. It is caused mostly by runoff of plant nutrients, such as nitrates and phosphates, from surrounding land.
