In 2012, the U.S. EPA approved the Lake St. Croix TMDL, calling for a 38% reduction in the phosphorus carried to the rivers and streams of the basin. The plan was implemented and published by MPCA (MN) and WDNR (WI) and still shows as active and ongoing in the WDNR website. Note this statement, this will require a net decrease of about 35 to 40% from point and non-point sources. The Total Maximum Daily Load, or TMDL report calls for a 38% reduction in the human-caused phosphorus carried to the rivers and streams of the basin, and eventually entering the St. Croix River and Lake St. Croix.
Lake St. Croix TMDL TMDL (wi.gov)
St. Croix Total Maximum Daily Load (TMDL) | A framework for water quality improvement | Wisconsin DNR
The St. Croix Lake Total Maximum Daily Load, or TMDL report, calls for a 38% reduction in the human-caused phosphorus carried to the rivers and streams of the basin, and eventually entering the St. Croix River and Lake St. Croix. 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.
Lake St. Croix TMDL implementation Plan (2013) was published by MPCA and WDNR 2013. Since the lake is currently impacted by phosphorus loading, resulting in algae blooms and eutrophication, the lake was placed on the TMDL priority list and implementation work is underway.
Rapid population growth and accompanying land-use changes have affected the water resources of the St. Croix River Basin. Based on a 39-percent projected population growth in the Basin by the year 2020, water resources will continue to degrade under the current circumstances. In response to this threat, the St. Croix Basin Planning Team conducted a detailed review of nutrient and sediment research and developed recommended water quality goals that would return Lake St. Croix to conditions that existed prior to 1950, before major ecological changes were experienced. These goals will require a 20-percent reduction in total phosphorus loading within the St. Croix Basin.
The overall goal is to reduce the inputs of phosphorus by 20% (100 metric tons) and return Lake St. Croix (the lower 25 miles of the river) to pre-1940’s conditions. After accounting for natural background levels, this will require a net decrease of about 35 to 40% from point and non-point sources. The Total Maximum Daily Load, or TMDL report calls for a 38% reduction in the human-caused phosphorus carried to the rivers and streams of the basin, and eventually entering the St. Croix River and Lake St. Croix. 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 watershed.
This TMDL was a collaborative effort among the Minnesota Pollution Control Agency (MPCA), Wisconsin Department of Natural Resources (WDNR) and the St. Croix Basin Water Resources Planning Team (St. Croix Basin Team). The primary components of the TMDL were largely based on the results of past lake and nutrient loading studies. The key outcomes of these studies and this TMDL are as follows:
Lake St. Croix total annual loading capacity needed to meet an in-lake total phosphorus water quality standard of 40 ug/L is 360 metric tons/yr.
The lakes 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.
In order to meet this reduction goal and restore Lake St. Croix water quality, communities and landowners in the St. Croix Basin will need to reduce storm water runoff from urban and agricultural land and limit wastewater treatment discharges. Restoration of water quality in Lake St. Croix depends upon local support as many phosphorus reduction activities will require voluntary efforts on privately owned land areas. Effective watershed management involves state and local government agencies, non-profit agencies and citizens all working together to sustainably manage local water resources.
USEPA decision document Lake St. Croix TMDL TMDL (wi.gov) TMDL tab
The U.S. Environmental Protection Agency has conducted a complete review of the final Total Maximum Daily Load (TMDL) for Lake St. Croix in eastern Minnesota (ID 82-0001) and western Wisconsin (ID 260 1500), including supporting documentation and follow up information submitted jointly by the Minnesota Pollution Control Agency (MPCA) and the Wisconsin Department of Natural Resources (WDNR). The St. Croix River and Lake St. Croix form a portion of the border between Minnesota and Wisconsin. The river flows southward into Lake St. Croix, which extends 24 miles downstream from Stillwater to Prescott, where it flows into the Mississippi River. The lake is located in Washington County, Minnesota and in St. Croix and Pierce Counties, Wisconsin. The TMDL was calculated for Total Phosphorus to address excess nutrients. 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). Because these are multi-jurisdictional waters, both Minnesota and Wisconsin concurred that the more stringent Minnesota standards be used in the development of this TMDL.
This TMDL meets the requirements of Section 303(d) of the Clean Water Act and EPA’s implementing regulations at 40 C.F.R Part 130. Therefore, EPA hereby approves Minnesota’s and Wisconsin’s one TMDL for total phosphorus. The statutory and regulatory requirements, and EPA’s review of Minnesota’s and Wisconsin’s compliance with each requirement, are described in the enclosed decision document.
USEPA Decision Document on the TMDL
Monitoring & assessments
The water quality in Lake St. Croix has been monitored for more than 30 years and will continue to be monitored for the foreseeable future. An extensive watershed program is also in place with different types of ongoing monitoring being conducted in different areas of the watershed. The St. Croix Basin Team will coordinate the ongoing monitoring efforts being conducted by the various agencies working throughout the watershed.