For over 40 years, Sweeney Lake homeowners operated a year-round artificial bubble-aeration system intending to oxygenate the water, improve conditions for native fish, and reduce the buildup of phosphorus and harmful algal growth in the impaired deep lake. However, water quality in the lake continued to decline, with notable improvements only during periods when the aerators were turned off. This raised concerns that the aeration system might be contributing to water quality issues rather than resolving them. The Minnesota Pollution Control Agency added Sweeney Lake to the impaired waters list in 2004 and the 2011 TMDL study identified the need to reduce internal and external phosphorus loading by 55% and 15%, respectively.
In response, the Bassett Creek Watershed Management Commission (BCWMC) engaged Barr Engineering Co. to investigate. Beginning in 2020, Barr collaborated with the BCWMC and the City of Golden Valley to evaluate the aeration system’s impact, develop educational factsheets, and facilitate stakeholder engagement to explore potential solutions.
Another approach to limiting in-lake cycling of nutrients was reducing common carp access and spawning in waters upstream of Sweeney Lake. Schaper Pond, located immediately upstream of the lake, was identified as a likely spawning and nursery area for carp. Barr conducted water-quality treatment-effectiveness monitoring, bathymetric surveys, and carp assessments. The results confirmed that carp activity was degrading the pond’s treatment performance, indicating a need for fish removal and consideration of passage control.
With federal grant funding secured by the commission, Barr and its subcontractors implemented a comprehensive restoration strategy to significantly reduce total phosphorus and improve water quality in Sweeney Lake. Our adaptive management approach involved multiple facets:
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Carp removal and long-term management
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A two-phase in-lake alum treatment
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Targeted herbicide treatment of curly-leaf pondweed
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Follow-up assessments of water quality and carp control in both Schaper Pond and Sweeney Lake
These actions addressed the final, critical sources of internal and external phosphorus loading, helping to meet the lake’s Total Maximum Daily Load (TMDL) targets and achieve both state and watershed goals for water quality improvement. Sweeney Lake was removed from the impaired waters list in 2024.