Excess nitrogen can also wreak havoc with the structure of ecosystems, affecting the number and kind of species found.

aquatic ecosystems in lakes, rivers, and coastal estuaries have probably suffered the most so far. They are the ultimate receptacles of much of the nutrient overload, which tends to accumulate in runoff or to be delivered directly in the form of raw or treated sewage. (Sewage is very high in nitrogen from protein in the human diet.) In these aquatic systems, excess nitrogen can often stimulate the growth of algae and other plants. When this extra plant matter dies and decays, it can rob the water of its dissolved oxygen, suffocating many aquatic organisms.

One of the more troubling aspects of this nutrient assault on aquatic systems has been a steady rise in toxic algal blooms, which can take a heavy toll on fish, seabirds, and marine mammals (Anderson 1994:62–68).