Plan to reduce phosphorus pollution approved by EPA

A coalition representing both sides of the river will now begin working to prevent runoff which hurts water quality.




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Algae in a backwater of the St. Croix River
Algae in a St. Croix River backwater (Photo by Randy Ferrin)

The United States Environmental Protection Agency recently approved the Total Maximum Daily Load (TMDL) for Lake St. Croix.

Under the regulations of the federal Clean Water Act, Lake St. Croix was declared an impaired water in 2008 by the States of Minnesota and Wisconsin, requiring that a TMDL report be written. The impairment is caused by excess phosphorus going into the lake, which enhances the growth of unwanted algae and thus changes the lake’s ecosystem and water quality.

Total water quality

A TMDL is a restoration plan to achieve a particular water quality goal. The TMDL is a complex formula that sets a limit on the amount of phosphorus coming from regulated sources like sewage treatment plants and large cities, and unregulated sources such as lawns, rural communities, and farm fields.  A margin of safety and a growth factor are built into the formula.

The TMDL was developed by the Minnesota Pollution Control Agency in conjunction with the Wisconsin Department of Natural Resources. The St. Croix Basin Water Resources Planning Team (The Basin Team) provided technical oversight and review. The Basin Team is a coalition of state, federal, county, and nonprofit organizations including the St. Croix River Association and has been in existence since 1993.

The Basin Team provided the technical data used in determining that Lake St. Croix was impaired.  In 2004, the Basin Team set a phosphorus reduction goal of 20 percent by the year 2020.  The two states agreed on that goal and signed a nutrient reduction agreement in 2006.  This agreement laid the foundation for the TMDL work.

Runoff reductions required

To achieve the restoration plan called for in the TMDL will require reducing phosphorus going into Lake St. Croix from the river’s 7600 square mile watershed.  More than 100 tons will need to remain in fields, lawns, and treatment plants to reach the goal.

An Implementation Plan was recently completed that shows where that reduction will need to occur, by county and by tributary watershed.  Much of the reduction will need to be by voluntary actions of land owners and farmers.

Although the target of the TMDL is to improve Lake St. Croix, many other lakes and streams in the St. Croix Basin will be improved through this work.  An educational campaign will be essential in providing the tools and knowledge to assist this effort.  For more information, check the links at the SCRA website or go to the MPCA website.

Randy Ferrin is the Basin Team Coordinator for the Lake St. Croix TMDL, and a board member of the St. Croix River Association.


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Plan to reduce phosphorus pollution approved by EPA