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 will be measured again in 2024 and carp may be removed through box netting, if needed.

Project Funding   |   Grant Funded

Estimated project costs are $568,080. Partial funding of $238,080 is proposed to 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 will be paid by a Federal Clean Water Act Section 319 grant awarded to the BCWMC through the Minnesota Pollution Control Agency.

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 is 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

Results from 2022 carp population assessment and water quality monitoring in Sweeney Lake are found in this memo. Water quality in the lake has improved significantly over the last 10 years. The lake is slated to be removed from the State's list of impaired waters in 2024! Carp populations will be reassessed in 2024. If needed, carp will be removed through baited box netting.

More Information

Final Grant Report to MPCA - May 2023

2022 Carp Population Assessment and Sweeney Lake Water Quality Results

Sweeney Lake Water Quality Improvement Project 2020 Activities and Outcomes Report for results from 2020.

2020 Carp Removal Results: Technical Memo

Curly-leaf Pondweed Treatment Areas (May 2020) ~ Wisconsin DNR Fact Sheet on Herbicide Diquat

Open House Presentation (April 8, 2020) Questions & Answers from Open House

Report and Presentation on Results of Carp Population Survey in Sweeney Lake and Schaper Pond

Resolution 19-09 Ordering Project (Sept 19, 2019)

319 Grant Workplan & Budget

Related Studies and Reports: