Plant nutrients, such as phosphates and nitrates, enter the water through sewage, and
livestock and fertilizer runoff. Phosphates and nitrates are also found in industrial wastes. Though these chemicals are natural, 80 percent of nitrates and 75 percent of
phosphates in water are human-added. When there is too much nitrogen or phosphorus
in a water supply (0.3 parts per million for nitrogen and 0.01 parts per million for
phosphorus), algae begin to develop. When algae blooms, the water can turn green and
cloudy, feel slimy, and smell bad. Weeds start to grow and bacteria spread.
Decomposing plants use up the oxygen in the water, disrupting the aquatic life, reducing
biodiversity, and even killing aquatic life. This process, called eutrophication, is a natural
process, but generally occurs over thousands of years. Eutrophication allows a lake to
age and become more nutrient-rich; without nutrient pollution, this may take 10,000
years, but pollution can make the process occur 100 to 1,000 times faster.