Nitrogen and phosphorus pollution, also called nutrient pollution, is a common impairment of lake water quality in Minnesota, and is responsible for the slimy, green algae blooms that are an all too familiar sight on our lakes in the summer. Nitrogen and phosphorus pollution is also responsible for the “dead zone” in the Gulf of Mexico, an area with little or no oxygen that cannot support marine life.

Excessive algae growth damages drinking water supplies, degrades the recreational and aesthetic values of our lakes, streams and rivers, and causes fish kills. Toxic algae blooms, called cyanobacteria or “blue-green” algae occur in nutrient-laden lakes in hot weather, and have proven fatal for livestock and pets. Damages to drinking water supplies have cost major metropolitan areas, including St. Paul, millions of dollars.  In humans, skin contact with blue-green algae toxins can cause itchy eyes and throat, skin rashes, and hives. Swimmers and other recreationists that ingest these blue-green algae toxins risk a variety of unpleasant to severe health problems, including stomach cramps, vomiting, diarrhea, fever, headache, severe muscle or joint pain, and seizures or convulsions.  Children are more vulnerable and may experience more severe reactions such as liver and central nervous system problems. Major sources of nutrient pollution include agricultural runoff and municipal wastewater discharge.

Excessive algae growth can also rob freshwater systems of the dissolved oxygen necessary to support a healthy fish community, resulting in fish kills.

Numeric water quality standards for phosphorus and algae—but not nitrogen—in Minnesota lakes were formally adopted by the Minnesota Pollution Control Agency and approved by US EPA in 2008. Lakes and reservoirs like Lake Pepin have been assessed and listed as impaired by excess nutrients using the same numeric limits since 2002.

Minnesota’s streams and rivers do not yet enjoy these same protections from excessive phosphorus, as the Minnesota Pollution Control Agency has not yet established numeric standards for nutrients in flowing waters. MPCA plans to release its draft standards for phosphorus and nitrate in streams and rivers for public comment in November 2011, with the new limits taking effect in late 2012.

In the interim, the MPCA is not calculating and imposing protective phosphorus limits in permits for dischargers to Minnesota’s lakes or rivers.  As a result, in October 2009, MCEA petitioned the US EPA to require corrective action, or in the alternative, de-delegation of the Minnesota Pollution Control Agency’s NPDES authorization.

Children playing in toxic cyanobacterial bloom, Lake Byllesby, Dakota County, Minnesota.
(Courtesy of Amy Goerwitz) 

Toxic algae bloom on Lake Crystal, Minnesota