Excess nutrients and harmful algal blooms create toxins and compounds in water that pose danger for human health.
There are several ways that people (and pets) can be exposed to these compounds.
Direct exposure to toxic algae
Stomach or liver illness
Nitrates in drinking water
Nitrate, a compound found in fertilizer, can enter drinking water in agricultural areas. A 2010 report on nutrients in ground and surface water by the U.S. Geological Survey found that nitrates were too high in 64 percent of shallow monitoring wells in agricultural and urban areas.
Infants are more susceptible to the health effects posed by nitrates, which can be serious and sometimes fatal.
Byproducts of water treatment
Stormwater runoff can carry nutrients directly into rivers, lakes and reservoirs, which serve as sources of drinking water for many people. When disinfectants used to treat drinking water react with toxic algae, harmful chemicals called dioxins can be created. These byproducts have been linked to serious health problems, including reproductive and developmental health risks.