Lake St. Croix TMDL


This TMDL is for Lake St. Croix on the St. Croix River, and is a joint submittal by both the Minnesota Pollution Control Agency (MPCA) and the Wisconsin Department of Natural Resources (WDNR). On April 6, 2006, an agreement was signed by Sheryl Corrigan, Commissioner of the Minnesota Pollution Control Agency (MPCA) and Scott Hassett, Secretary, WDNR, committing their agencies to work cooperatively to achieve the 20-percent phosphorus reduction goal. This goal will form the basis for future TMDL and implementation efforts.


The TMDL sets goals for each watershed in the basin, based on the respective land cover and land uses practices. It also sets a cap on the amount of phosphorus that can be discharged each year by wastewater treatment plants serving communities and industries in the St. Croix Basin.


The key outcomes of these studies and this TMDL are as follows: (1) Lake St. Croix’s total annual loading capacity needed to meet an in-lake total phosphorus water quality standard of 40 µg/L is 360 metric tons/yr. (2) The lake’s “current” loading (using a 1990s baseline) is 460 metric tons/yr, meaning a 100 metric ton/yr reduction would be needed. However, this TMDL adopts a margin of safety and a reserve capacity which increases the needed load reduction to about 123 metric tons/yr. This equates to an overall needed phosphorus load reduction of 27 percent.

QA Measures

Run Project Summary Report

TMDL/303d Projects
Implement TMDL
Lake St. Croix TMDL
Reports and Documents
Implementation Plan for the Lake St. Croix Nutrient TMDL
The approval letter and decision document written by the EPA for the Lake Saint Croix TMDL.
Lake Saint Croix Nutrient Total Maximum Daily Load, May 2012. Colaboration between the Minnesota Pollution Control Agency and the Wisconsin Department of Natural Resources.
The Stakeholder Strategy and Communitcation Plan describes people's response on how they view their engagement in the TMDL process for Lake St. Croix and outlines what may be the challenges for implementing the TMDL. It also helps understand what everyone's role in the St. Croix Basin is, and who they should be working with as activities to reduce nutrients move forward.
Data Documentation
Activities & Recommendations
TMDL (USEPA) Approved
EPA approves Minnesota's and Wisconsin's one TMDL for total phosphorus on Lake St. Croix. The designated use impairment in the lake is aquatic recreational use, and Lake St. Croix is classified as a Class 2B water and is defined as and protected for aquatic life (warm and cool water fisheries and associated biota) and recreation (all water recreation activities including bathing).
TMDL Development
TMDL Development for Lake St. Croix addressing phosphorus impairment.
TMDL Implementation
Move the TMDL from draft to approved and begin implementation.