WATER QUALITY MONITORING
Water Quality Monitoring
The Minnesota Pollution Control Agency (MPCA) conducts water quality assessments as a part of a watershed monitoring program to determine the condition of surface waters in the state. These assessments show that the Le Sueur is similar to its neighbors in southern Minnesota, with stressors of elevated nutrients and fish bioassessment resulting in most of the impairments in lakes.
Watershed Pollutant Load Monitoring Network
There are six long term water quality monitoring sites in the Le Sueur River Watershed that are part of the Watershed Pollutant Load Monitoring Network (WPLMN).
Due to the often-negative impact the Le Sueur River has on downstream waters, the MPCA installed six Watershed Pollutant Load Monitoring Network (WPLMN) sites to better understand water quality and pollutant loading dynamics within the watershed. The long-term nature of these stations is critical for trend analysis, measuring between-year differences in pollutant loading, and helping determine pollutant sources and their contributions.
All WPLMN sites within the Le Sueur River Watershed have much higher than desired levels of sediment and nutrients. All sites show relativity consistent concentrations of elevated nitrate-nitrogen. Phosphorus concentrations and loads are also very high throughout the watershed with levels increasing even more as waters flow through the lower sections of the watershed. This is likely a result of phosphorus attached to the additional sediment picked up along these lower sections. Average sediment concentrations are much too high to support the water quality standard with the exception of the Maple River. The Maple River site receives cleaner water from lakes and wetlands within the drainage area, helping to keep sediment concentrations low. Average sediment concentrations at the outlet of the Le Sueur River are very high compared to other watersheds in the region and state; more than four times the water quality standard.
The Le Sueur contributes disproportionately high pollutant loads to the Upper Mississippi River basin when compared to other contributing watersheds. For example, the Le Sueur River Watershed accounts for less than 2% of the total drainage area above Lock and Dam 3 near Red Wing, Minnesota, the furthest downstream monitoring site on the Mississippi River above Lake Pepin. Yet it contributes the equivalent of 28% of the sediment load measured at Lock and Dam 3. Nitrate-nitrogen and phosphorus contributions from the Le Sueur have a lesser impact than sediment loads, but are still approximately 11% of the average load at Lock and Dam 3 (MPCA, 2021).
Learn more about the WPLMN:
View WPLMN Monitoring Data
Major Watershed Site:
Le Sueur River Near Rapidan, CR8
Le Sueur River at St. Clair
Big Cobb River near Beauford
Maple River near Sterling Center
Learn about the Watershed Approach
Learn about MPCA Citizen Water Monitoring In Minnesota
Water Quality Impairments
Streams have various pollutants or stressors of turbidity, nutrients, E. coli/fecal coliform, fish and macroinvertebrates bioassessments. In total, there are 133 impairments from 7 lakes and 28 streams within the watershed. Of these impairments 110 are for aquatic recreation based on criteria for the area. The remaining impairments are for aquatic consumption, which has a state wide criteria.
Of the 74 stream sections examined, only one- in the Cobb River- supported aquatic life; 21 were impaired; 12 need more data to determine their status; and 40 have been altered significantly so the MPCA is deferring assessment. Under federal and state laws, impaired waters must have Total Maximum Daily Load (TMDL) studies to determine reductions of pollutants needed to again meet water quality standards. In this first Watershed Restoration and Protection Strategy (WRAPS) cycle, the MPCA completed TMDL studies for four lakes and six stream sections. In addition to these lakes and stream sections, the MPCA has completed a TMDL study for Lura Lake in the watershed and a TMDL study of turbidity in the Le Sueur River as part of the Greater Blue Earth River system.
There are 72 lakes in the watershed. Most lakes did not have sufficient data to make a formal assessment. Of the 11 lakes examined in the watershed. Of these lakes, Reeds and St Olaf were found to be fully supporting recreational use but both do have an aquatic consumption impairment due to mercury in fish tissue. Five lakes (Eagle, Elysian, Freeborn, Madison, and Lura) were impaired due to high nutrient levels for impacts to aquatic recreation and aquatic life due to nutrients and fish bioassessments. Four lakes needed more data to determine their status. There are no known significant water control structures on our lakes and rivers, however, there are dams controlling the outlets on multiple lakes, such as Elysian, Buffalo, Silver, Eagle, Madison and Freeborn. Fish barriers are on the outlets of Freeborn Lake and Lake Elysian. (Source: Le Sueur River Watershed WRAPS Report)
Le Sueur River Watershed Website (MPCA)