This process is called eutrophication. Lower oxygen levels can stress fish and aquatic insects, possibly even causing pollution sensitive creatures to leave or die. See the dissolved oxygen information sheet to learn more about the importance of oxygen in a stream. Excretions of aquatic organisms can be very rich in ammonia, but unless a stream is overpopulated with organisms, the levels of ammonia in a stream will not rise. Some lakes and ponds have large ammonia loads added from the excrement of large goose and duck populations, whose natural predators may have been eliminated by man.
Cattle also can have a similar response when drinking nitrate contaminated water.
A summary of these data is below to provide an understanding of past values of nitrates and demonstrate trends or relationships of past total nitrate concentrations.