Much of the river has been straightened and altered to provide for drainage of farmland and for flood reduction. Though the vast majority of the Watonwan watershed is used for farming, mainly corn and soybeans, small lakes and wetlands provide significant habitat for waterfowl.
Like most areas of the Minnesota River Basin, the soils in the Watonwan River watershed are highly erodible. Changes in climate and changes in the landscape have resulted in higher flows in the river system. The combination of erodible soils and higher flows has led to greater levels of erosion and a dramatic increase in sediment levels in the river system since European settlement in the late 1800s. Sediment makes the water cloudy and hurts aquatic life such as fish.
The Watonwan River, along with the LeSueur River, are the Blue Earth River's largest tributaries. Together, these watersheds make up the Greater Blue Earth River Basin, which drains 5,540 square miles (2.3 million acres) in 11 counties in Minnesota and three in Iowa.
By volume, the Blue Earth is the Minnesota River's largest tributary, accounting for 46 percent of the Minnesota's flow at the rivers' confluence. It also a major contributor of sediment to the Minnesota River. In the Greater Blue Earth River Basin, 39 sections of streams and rivers fail to meet the state water quality standard for turbidity, meaning the water is too cloudy and affects aquatic life such as fish.
Several stretches of streams in the Greater Blue Earth River also have bacteria levels high enough to violate the state water quality standard, indicating they are not suitable for swimming and other body-contact recreation. Restoring these streams will require reducing bacteria levels by 80 to 90 percent.
What's being done
Strategy development for restoration and protection
The MPCA is working with local partners, focusing on feedlots and failing septic systems, to reduce bacteria levels and make streams suitable for swimming and other body-contact recreation. As part of the Minnesota River Basin, the Blue Earth and its tributaries have been the subject of several scientific studies, including research by the MPCA, WRC-Minnesota State University-Mankato, University of Minnesota, National Center for Earth Surface Dynamics, Minnesota Department of Agriculture, and others.
- Watonwan River Watershed WRAPS Report (wq-ws4-62a)
- Summary - Watonwan River Watershed Restoration and Protection Strategy report (wq-ws4-62b)
- Watonwan River Watershed TMDL Report (wq-iw7-52b)
- Public comment period for the draft WRAPS and TMDL is July 22 to September 20, 2019
Monitoring and assessment
The MPCA finished intensive water monitoring of the Watonwan watershed in 2016. A summary of that report is included in the links below. Intensive monitoring will resume again in 2023 to monitor and reassess watershed health.
The MPCA and several other agencies monitor the water quality of the rivers and streams in the watershed, an effort that spans more than 20 years.
Water quality model supporting documents
- Model resegmentation and extension for Minnesota River watershed model applications
- Hydrology and water-quality calibration and validation of Minnesota River watershed model
- Watonwan River HSPF Summary (wq-ws3-07020010c)
- Minnesota River Basin HSPF Model Hydrology Recalibration (wq-iw7-47q)
- Minnesota River Basin Sediment Delivery Analysis (Final) (wq-iw7-47p)
- Minnesota River Basin HSPF Model Sediment Recalibration (wq-iw7-47o)
The Watonwan River Watershed Restoration and Protection Strategies (WRAPS) report summarizes the MPCA’s Watershed Approach work findings of the status of surface waters in the Watonwan River Watershed. This work relied on local watershed partners (soil and water conservation districts [SWCDs], counties, and other state agencies) and civic engagement processes to identify challenges, opportunities, and recommendations to achieve higher adoption of conservation practices within the watershed.
Several water body pollutants and stressors were identified. A source assessment, goals, and 10-year targets were developed for each pollutant and stressor and are summarized in the WRAPS report. Identified strategies include: Improving soil health with cover crops and reduced tillage, improving manure and fertilizer application, and improving stream riparian habitat. Priority areas to focus restoration and protection efforts include: Barely impaired waters, protecting supporting waters, drinking/ground water, and critical wildlife habitat.
Intense storms of late spring can wash soil and other pollutants into rivers. Producers can use several techniques to protect their soil and water quality.