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.
Under state standards, the level of Total Suspended Solids for rivers in the basin should be 90 parts per million. However, levels average between 175 to 675 parts per million, far above the levels needed for clear water, according to water monitoring from 2000-2008.
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
Monitoring and assessment
The MPCA has finished intensive water monitoring of the Watonwan watershed and plans to publish a report on this effort in 2016. As part of this project, the agency has also started work to identify stressors hurting water quality and conditions fostering healthy waters. In addition, the MPCA, Greater Blue Earth River Basin Alliance, and Water Resources Center-Mankato are gathering input from citizens in the watershed through interviews and events.
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)
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.
The MPCA and Water Resources Center of Minnesota State University-Minnesota are finalizing a Total Maximum Daily Load report for the Greater Blue Earth River Basin. In this report, the MPCA recommends a 0% reduction in sediment levels during low flow conditions and a 92.7% reduction during high flow conditions such as spring thaw. After the report goes on public notice and receives approval from the U.S. Environmental Protection Agency, the MPCA and Water Resources Center will work with stakeholders and scientists to develop an implementation plan to guide restoration.
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.