Excess phosphorus is harming Minnesota waters. Phosphorus comes from both regulated and non-regulated sources. A quarter of Minnesota lakes have high levels of phosphorus, which means that they do not meet water quality standards for recreation. Excess phosphorus feeds algae growth that makes waters less attractive for swimming and other aquatic recreation. It degrades the conditions that fish, bugs, wildlife, and desired plants need to thrive. In addition, phosphorus can fuel toxic blue-green algal blooms, which are harmful to people and pets.
Phosphorus is a common element in agricultural fertilizers, manure, and organic wastes in sewage and industrial discharges.
Rain and snowmelt can wash fertilizers and manure off agricultural land and into ditches, streams, and lakes. It can also be in discharges of treated wastewater from communities and businesses. Erosion of soil and other particles is another source of phosphorus, which binds to sediment. Reducing any runoff, including hard surfaces in urban areas and cropland in rural areas, is an important strategy for reducing phosphorus in lakes and streams.
Human health and environmental concerns
Lakes, rivers, and streams with excess phosphorus can grow algae, which sets off a vicious cycle:
- Algae blooming can hinder recreation such as swimming, while also damaging habitat for fish and other aquatic species
- As algae decay, they use up oxygen in the water, leaving less to sustain fish and other aquatic species
- In addition, algae release more phosphorus into the water as they decay, providing more fuel for additional algal blooms
- Some algae contain a bacteria that can be toxic to people and pets
Minnesota is a headwaters state, meaning major river systems start here and flow into other states and Canada. The Mississippi River empties into the Gulf of Mexico, the Red River flows into Lake Winnipeg in Canada, and several rivers in northeast Minnesota run into Lake Superior. Our nutrient pollution impacts millions of people downstream, including those who depend on rivers for drinking water. To help waters here and downstream, Minnesota has adopted a nutrient reduction strategy that outlines goals and action steps for reducing phosphorus and nitrogen.
Impact of climate change
Minnesota is receiving more precipitation in intense storms that leads to more runoff, which in turn leads to more phosphorus in lakes and rivers. Also, longer periods of hotter temperatures are raising lake water temperatures, increasing the potential for algal blooms, including toxic blooms.
Monitoring, reporting, and regulations
A quarter of Minnesota lakes have high levels of phosphorus. The MPCA designates bodies of water that have excess phosphorus as "impaired." The agency both identifies the sources of phosphorus and the reductions needed to meet water quality standards for impaired waters.
Even if a body of water has high levels of phosphorus, it can still be suitable for recreation. Algae generally blooms in hot, calm weather and may be disrupted by rain and winds.
Reducing phosphorus pollution requires continual long-term strategies, but all Minnesotans can take action to protect our lakes and streams.
- Using less fertilizer on lawns, cropland, and other areas and using management practices such as buffer strips that filter runoff
- Following feedlot operation and manure application rules to prevent runoff, such as mandatory setbacks from bodies of water and avoiding applications during rainy weather
- Using phosphorus-free lawn fertilizer
- Complying with phosphorus discharge limits at wastewater treatment facilities
- See the Reducing phosphorus pollution web page for more