Lake St. Croix TMDL
TMDL Development
Approved TMDL
Implement TMDL
Evaluate for Delisting

Project Description

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.

Project Goals

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 Basin.


Kathy Bartilson
Paul LaLiberte
Buzz Sorge

Project Plan

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.

What's New

Lake St. Croix TMDL implementation Plan (2013) (updates will be posted here as they are available).
Lake St. Croix TMDL Stakeholder Engagement Strategy and Communication Plan, May 2011

Partners, Stakeholders, Team Members

The St. Croix Basin Water Resources Planning Team has been involved in goal setting and TMDL development over the past several years. This group includes state, local and federal agencies and partners from both Wisconsin and Minnesota. The TMDL covers loadings and reduction goals by sub-watershed for each state, as well as point source limits for all dischargers with specific permits. Minnesota Pollution Control Agency (MPCA) staff have been equally involved in the creation of the TMDL and interstate agreements. St. Croix Basin Water Resources Planning Team, Science Museum of Minnesota, St. Croix Watershed Research Station, and Barr Engineering Company.

Resource Conditions

The St. Croix River basin represents a large area approximately 7,760 square miles with 44 percent of the basin land area (excluding water and wetlands) located within Minnesota and 56 percent within Wisconsin. It includes portions of the Northern Lakes and Forests (NLF), North Central Hardwood Forests (NCHF) and a small portion of the Western Corn Belt Plains (WCBP) ecoregions. The St. Croix River originates near Solon Springs, Wisconsin, and flows west and south more than 160 miles until it joins the Mississippi River at Prescott, Wisconsin. Lake St. Croix is a naturally impounded riverine lake in the lower 25 miles of the St. Croix River.

The St. Croix River is a sixth-order stream, draining an area of 20,098 square kilometers (7,760 square miles). The river is largely free-flowing with the exception of a four meter high dam at Gordon, WI which impounds 774 ha of water in the main-stem, and an 18 meter high hydroelectric dam at St. Croix Falls, WI and Taylor Falls, MN which impounds 314 ha. The final 26.4 km of the main-stem includes Lake St. Croix, a natural lake covering 1,889 ha. The lake formed after the formation of an eight kilometer land spur which narrows the river channel to 0.2 km. The water level in the lake is significantly influenced by the Mississippi River. Average annual mean discharge at St. Croix Falls from 1931 to 1982 was 120 cubic meters per second (m3/sec), or 4,238 Minnesota Pollution Control Agency Lake St. Croix TMDL cubic feet per second (cfs). The permitted design flows of wastewater facilities in the basin total 38.6 million gallons per day. (This total excludes the very large cooling water discharge from the Xcel Alan S. King Power Plant since the cooling water is also withdrawn directly from the St. Croix.) The total wastewater flow is equal to 60 cfs, or less than 1.5% of the annual mean discharge. Groundwater contributions stabilize flows during periods of low precipitation.

Priority Waters

The St. Croix River and Lake St. Croix are highly valued resources that provide exceptional recreational opportunities and support a highly diverse ecology of aquatic and terrestrial species. However, over the years eutrophication, or nutrient enrichment, has occurred in Lake St. Croix due to excess phosphorus loading. This loading drives nuisance algae blooms which diminish the enjoyment and use of the lake. This report represents an important step in the improvement of Lake St. Croix by focusing on establishing the needed reduction in the loading of phosphorus from its contributing basin in order to achieve water quality standards.

Interactive Viewer

  • Restoration Viewer This interactive webmapping application displays mapping products specifically for TMDL implementation.
  • Surface Water Data Viewer The Surface Water Data Viewer is a generalized interactive mapping application that displays a wide variety of water related datasets.
  • Water Condition Viewer The Water Condition Viewer provides monitoring, assessments, and management datasets for water quality.

GIS Maps

GIS map of the TMDL Projects in Wisconsin
Wisconsin's Total Maximum Daily Loads

Final TMDL

Lake St. Croix Nutrient Total Maximum Daily Load, published May 2012, Prepared in Partnership by Minnesota Pollution Control Agency and the Wisconsin Department of Natural Resources with the St. Croix Basin Water Resources Planning Team, Science Museum of Minnesota, St. Croix Watershed Research Station, and Barr Engineering Company
Final TMDL

Public Comment

EPA policy is that there should be full and meaningful public participation in the TMDL development process. The TMDL regulations require that each State/Tribe must subject calculations to establish TMDLs to public review consistent with its own continuing planning process (40 C.F.R. �130.7(c)(l)(ii)). In guidance, EPA has explained that final TMDLs submitted to EPA for review and approval should describe the State's/Tribe' s public participation process, including a summary of significant comments and the State's/Tribe's responses to those comments. When EPA establishes a TMDL, EPA regulations require EPA to publish a notice seeking public comment (40 C.F.R. �130.7(d)(2)).

Provision of inadequate public participation may be a basis for disapproving a TMDL. If EPA determines that a State/Tribe has not provided adequate public participation, EPA may defer its approval action until adequate public participation has been provided for, either by the State/Tribe or by EPA.

The TMDL was public noticed from December 12, 2011 to January 11, 2012. Past participation and communication is documented in Section 9 of the TMDL. There were many meetings within the watershed with permitees, citizens, and stakeholder groups, occurring at different times and locations. The schedule enabled many persons to have access to the meetings in both states all across the watershed.

USEPA Decision Document

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

About TMDLs

South Fork Eau Claire River, Lisa HelmuthWisconsin's TMDL Program is working on a variety of flyers and handouts to support a common understanding of the state's TMDL process and requirements. Overview of TMDLs [TMDL Page]

What is a TMDL [PDF]
A Total Maximum Daily Load (TMDL) is the maximum amount of a pollutant that a body of water can receive while still meeting water quality standards. A waterway that exceeds standards is often no longer suitable for its designated uses, such as wildlife habitat, fishing, or other recreational activities.

Frequently Asked Questions (FAQs)[PDF]
"Why do we need to create TMDLs?", "What is an "impaired water"?", and "How is a TMDL implemented?"

Education & Outreach

During the implementation phase, partners will work together to identify the most effective approach to design an innovative public education program that will promote community awareness and clearly identify the contribution that all basin citizens must make to reduce nutrient loading. Any new public education and outreach activities related to water quality issues will build on existing programs currently implemented by local partners. A successful education and community outreach program will also include:

  • Continuation of the annual Protecting the St. Croix Conference; used to communicate progress toward meeting the basin goals and the TMDL implementation goals.

  • Homeowner education about specific, targeted phosphorus reduction opportunities such as composting, rain gardens and rain barrels.

  • Collaborative working relationships with organizations actively involved in environmental education such as Northland NEMO, Watershed Partners, and others.

  • Collaborative work with citizen-led environmental organizations such as local lake associations.

  • Continued outreach to the agricultural community through collaboration with producers, farm organizations, crop consultants, Land Conservation Departments, Soil and Water Conservation Districts, University Extension staff, Watershed Districts, producer-led councils, and other affiliated groups.


DNR Water Webinars [Go to Webinar Page]

Trading and Adaptive Management
UW Extension Webinars on Adaptive Mangement [exit DNR]

Water Quality Trading & Adaptive Management
The Basics || PDF Format
Finding, Quantifying Credits || PDF Format
Developing a Plan || PDF Format
Implementing and Verifying Offsets || PDF Format

Understanding Phosphorus Rules & Management Options
Adaptive Management Basics [3/3/12]
Phosphorus Discharge Limits [3/3/12]
Complying with Phosphorus Discharge Limits [3/28/12]
Water Quality Trading Framework Update [2/10/11]

Clean Water Act: Water Quality Report to Congress
Impaired Waters List Updates, 2014
Water Quality Report to Congress Webinar 2012
Water Quality Report to Congress: Impaired Waters & Water Quality Planning [12/05/11]
Water Quality Management Planning July 2010-11 [07/13/10]
Water Quailty Report to Congress & Website Overview [12/09]

Monitoring and 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. The monitoring goals determined by the St. Croix Basin Team include:

  • Determining nutrient and sediment concentration trends and loads for the main stem of the St. Croix River and Lake St. Croix.
  • Determine nutrient and sediment loads for the selected tributaries used to track progress on tributary nutrient-management goals.
  • Determine trends in biological indicators in Lake St. Croix, Lake Mallalieu, and at main-stem and tributary locations.
  • Provide information used in the development and calibration of main stem and tributary nutrient models.

Monitoring is based on an ideal monitoring network, detailed in the Monitoring Plan for the St. Croix River: 2010 (VanderMeulen, D., 2010). The monitoring sites have been selected to achieve the goals stated above. The desired monitoring scheme and parameters, based on the four goals outlined above, are shown below:

Monitoring Objective 1: Mainstem and Lake St. Croix Water Quality A minimum of five monitoring sites from within the main stem of the St. Croix River and Lake St. Croix, Continuous flow gauging, baseflow and storm-composite sample analysis for sediment and nutrient variables.

Monitoring Objective 2: Tributary Loads Up to 23 sites for individual tributaries will be monitored,base-flow and storm-composite sample analysis for sediment and nutrient variables.

Monitoring Objective 3: Algal Response Seven monitoring sites within the pools of Lake St. Croix and Lake Mallalieu,Semi-monthly (May-September) sample collection and analysis for Secchi depth, dissolved organic, carbon, chlorophyll-a, and phytoplankton biomass and composition, Sediment sample collection and analysis every third year for diatom biomass and composition.

Monitoring Objective 4: Subwatershed Load Distribution One to four monitoring sites targeted for each sub-watershed,Continuous flow gauging,Base-flow and storm-composite sample analysis for a conservative tracer (chloride) and sediment, and nutrient variables. The comparison between future monitoring data and the modeling results in this study can be conducted as follows:

Using monitoring results (flow and water quality sampling data), calculate the annual load (or the load over some other time period) of phosphorus leaving the monitored basins, Run the in-lake models for same time period and calculate the load that the model predicts for pre-project conditions,Compare the two loads, and calculate the percent reduction that was achieved over the time period of interest.

Agriculture (CAFOs, Runoff) Group

Water quality impacts and phosphorus loadings are dependent on animal manure handling, crop rotations, fertilizer application rates and practices (nutrient management), tillage practices, and precipitation frequency and intensity. Improvements will be needed in all of the farming practices listed above to lower the agricultural loading, especially in the watersheds with the highest loadings (the Apple, Kinnickinnic, Willow, Snake and Sunrise). Some other recommended reduction strategies include:

  • Develop comprehensive nutrient management plans for all agricultural croplands in the basin.
  • Directing drainage from confined livestock areas to retention basins, grassed buffer strips, constructed wetlands, or other effective nutrient-reduction practices.
  • Use of holding areas and wintering areas for livestock, on a rotational basis, to prevent a build-up of nutrients in the soil. Remove manure accumulated in confined holding areas regularly and apply to crop or pasture lands at agronomic rates.
  • Develop regional nutrient budgets to assist in siting intensive livestock operations and develop practical options for treating and exporting manure to nutrient-deficient areas.
  • Consider new tile drainage systems, such as controlled drainage, to regulate the quantity of water removed at different times of the year.
  • Work with all sectors of the agricultural community to implement new advances in agronomy, soil conservation, nutrient management, etc.

Stormwater Group

Successful stormwater management includes implementation of local planning and zoning ordinances, codes, and policies, ideally including standards for treatment that:

  • Incorporate low-impact development concepts into future land-use planning and stormwater treatment to reduce pollutant loading and maintain hydrologic integrity for all new development, redevelopment, industrial, and construction sites.
  • Establish zoning regulations, such as minimum set-back distances from shorelines for new developments and redevelopment, to prevent significant disturbances which would result in increased erosion along lakes and waterways.
  • Incorporate low-impact design principles into all plans for re-development or expansion and infrastructure or street replacement projects to treat existing sources of stormwater that are not subject to other permit programs.
  • Where it is not feasible or cost-effective to improve the existing developed hydrology and pollutant loadings, other options for providing regional management of stormwater runoff should be explored.

In response to the growing need for stormwater BMP performance standards, in 2009 the Minnesota legislature allocated funds to develop performance standards, design standards or other tools to enable and promote the implementation of low impact development and other stormwater management techniques. The Minimal Impact Design Standards (MIDS) project represents the next generation in stormwater management and will develop tools to assist communities in meeting water quality goals. The three main elements of MIDS at this time are: a higher clean water performance goal, new modeling methods and calculations, and a credits system and ordinance package.

MS4 permittees in Wisconsin will be reducing total suspended solids (TSS) by 20 percent in established areas from the "no-control" scenario as required by the Wisconsin MS4 General Permit. Operations involving new construction (both inside and outside of MS4 areas) are required to reduce TSS by 80% (compared with no controls) under the Wisconsin Construction Site General Permit. Reduction of TSS will provide significant reduction of associated phosphorus.

To demonstrate compliance with their WLAs, MS4 permittees will have the option to select from a suite of Best Management Practices (BMPs), which will be developed collaboratively during implementation planning, and will be used as part of a performance-based compliance approach. Because this TMDL used the decade of the 1990s as a baseline for determining ?current? loading there will be a need to determine load reductions that have occurred since that time in order to determine needed reductions to achieve allocations.

Construction stormwater activities in Minnesota are considered in compliance with provisions of the TMDL if they obtain a Construction General Permit under the NPDES program and properly select, install and maintain all BMPs required under the permit, including any applicable additional BMPs required in Appendix A of the Construction General Permit for discharges to impaired waters, or meet local construction stormwater requirements if they are more restrictive than requirements of the State General Permit.

Industrial stormwater activities in Minnesota are considered in compliance with provisions of the TMDL if they obtain an industrial stormwater general permit or General Sand and Gravel general permit (MNG49) under the NPDES program and properly select, install and maintain all BMPs required under the permit.