Projects

Sweeney Lake Water Quality Improvement Project

Golden Valley

Project Number: SL-8

Project Status | Complete

The BCWMC officially ordered this project at their meeting on September 19, 2019 after a public hearing. (There were no public comments regarding this project received during the hearing.) The federal grant for this project was approved and a grant agreement was executed in January 2020. A survey of aquatic plants and an herbicide treatment of curly-leaf pondweed took place in spring 2020. Carp management in Sweeney Lake and Schaper Pond, including removing carp with baited box nets, took place summer 2020. The first treatment with alum was applied in late October and early November 2020. A second alum treatment was applied in fall 2022. The carp population in Schaper Pond and Sweeney Lake were reassessed in 2022. Carp numbers rebounded slightly from the low numbers measured after the 2020 carp removal efforts, but remain below the threshold known to impact water quality. Carp populations were measured again in 2024. Due to their high numbers, 191 carp were netted and removed from Sweeney Lake, weighing a total of 1,473 pounds, which represented an estimated 42.5% of the carp biomass in the lake. After carp removal, the estimated carp biomass density in the lake was reduced to 31 kg/ha, well below the threshold 100 kg/ha known to impact lake water quality. Additional carp surveys will be completed in 2026.

Project Funding | Grant Funded

Estimated project costs totaled $568,064 with funding of $238,080 is come from the BCWMC’s Capital Improvement Program funds through 2020 and 2021 ad valorem property taxes collected by Hennepin County on property within the Bassett Creek Watershed. The remainder of project costs were paid by a Federal Clean Water Act Section 319 grant awarded to the BCWMC through the Minnesota Pollution Control Agency.

Funding for additional carp surveys, carp removals, and water quality monitoring in Sweeney Lake and Schaper Pond (immediately upstream from Sweeney Lake) come from the Schaper Pond Diversion Project CIP.

Project Description

This project significantly reduced phosphorus, improved water quality, and supported a balanced aquatic ecosystem in Sweeney Lake through alum treatments and managing carp in Schaper Pond (just south of the lake) and in Sweeney Lake. Sweeney Lake is a 67-acre lake with a maximum depth of 25 feet and an average depth of 12 feet. The lake provides recreational value for fishing, boating, and swimming; and it harbors a variety of panfish, a limited game fishery, and an average plant community. The lake receives runoff from a 2,400-acre fully developed watershed with nearly all of the flow entering through the Sweeney Branch of Bassett Creek. The creek flows from the south and through Schaper Pond which is immediately upstream of Sweeney Lake. Despite numerous best management practices installed or implemented in the lake's watershed over the years, water quality in Sweeney Lake had not improved significantly. Regular monitoring from 1985 to the present indicates that total phosphorus concentrations exceeded the state standard of 40 ug/L 74% of the time. Further, the lake had a history of Harmful Algae Blooms, negatively impacting the lake’s recreational usability.

In 2018 the Sweeney Lake Association agreed to turn off the year-round aerators that had been running for decades. That action certainly helped improve water quality. This project further reduced total phosphorus in the lake with a combination of curly-leaf pondweed control in Sweeney Lake, carp management in Schaper Pond and Sweeney Lake, and an alum treatment in Sweeney Lake. The goal was to effectively “flip” this lake from a eutrophic, algae dominated system, to a healthy, clear water system that can fully support aquatic recreation and a balanced ecosystem for aquatic biota.

Project Announcements

This project is complete although carp surveys and removals continue. Results from 2024 carp population assessment and removals in Sweeney Lake are found in this memo. The lake was removed from the State's list of impaired waters in 2024 due to significant improvements in water quality.