EPA Approves Total Maximum Daily Load Study To Improve Water Quality For Lake Pepin, Tributaries

MADISON, Wis. – The Wisconsin Department of Natural Resources (DNR) announced that on July 21, 2026, the United States Environmental Protection Agency (U.S. EPA) approved the Lake Pepin TMDL: Total Maximum Daily Loads for Total Phosphorus study.

The DNR, together with many partners throughout the basin, including the Minnesota Pollution Control Agency (MPCA), continues working to improve the water quality of Lake Pepin and its tributaries.

Lake Pepin, bordered by Minnesota to the west and Wisconsin on the east, is located just south of where the St. Croix and Minnesota rivers join the Mississippi River. Lake Pepin and two small streams that drain directly to it, Lost and Bogus creeks, are listed on Wisconsin’s 303(d) list as impaired due to excessive phosphorus.

Impaired waters in Wisconsin are largely addressed through an analysis known as a Total Maximum Daily Load (TMDL). A TMDL evaluates the amount of pollutant a waterbody can receive and still meet water quality standards. This TMDL study is designed to complement the MPCA’s TMDL, approved by the U.S. EPA in May 2021, by addressing Wisconsin’s portion of the Lake Pepin drainage basin. 

The multi-year TMDL study received federal funding and U.S. EPA contractor support. Tetra Tech, a U.S. EPA-funded contractor, conducted a detailed watershed survey of agricultural cropping, tillage and management practices and translated allowable phosphorus loads for agricultural sources into a format consistent with commonly used implementation models, such as Wisconsin’s nutrient management software, SnapPlus. The DNR also worked with County Land and Water departments to evaluate implementation mechanisms and dovetail this information with ongoing conservation efforts. 

"I am grateful for the U.S. EPA’s assistance on this project," said Adrian Stocks, Director of the DNR’s Water Quality Bureau. "The DNR’s efforts were able to build on the great work already conducted by MPCA. Analysis shows that with management measures and strategic deployment of resources, water quality standards can be attained and protected, further supporting and enhancing the abundant recreational activities of the region as well as maintaining agricultural production."

The DNR will continue to work with partners throughout the Lake Pepin basin to reduce pollution while also providing agricultural producers and wastewater dischargers with the support they need to implement management measures.

Copies of the TMDL study and supporting information can be found on the DNR website.