Overview

Lake Delavan is a moderately large eutrophic lake in Walworth County. A dam on Swan Creek, the lake's outlet stream, elevates the lake level by three feet. Due to excess nutrients the lake has been plagued for years by poor water quality, severe blue-green algae blooms, excessive populations of rough fish, anoxic conditions and fishkills. Construction of a municipal sewer system eliminated septic systems surrounding the lake by 1981 and a complete restoration was attempted in the late 1980s and 1990s. The restoration included dewatering, pesticide application for carp removal, and extensive alum treatments. However, tons of phosphorus and nutrient-rich sediments remain in the lake.

Although the lake's excess nutrients no longer result in the large blue-green algae mats of the 1970s and 1980s, an overabundant fishery and excessive populations of Eurasian water milfoil are now problematic. An Aquatic Plant Management Plan was completed for the lake in 1993 by Aron & Associates. In 1975, more than 15 percent of the lake's direct drainage was urbanized; today this percentage is likely higher. Plans for a new dog track and numerous new subdivisions in the direct drainage area ensure that stormwater management, construction site erosion, and hydrologic modification will be top concerns for this lake in the coming years.

The Lake Restoration Project implemented by local citizens, governmental units, the University of Wisconsin, WDNR, U.S. Geologic Survey and U.S. Environmental Protection Agency in the 1980s and 1990s included the following milestones: short-circuiting the mixing of nutrients coming into the lake from Jackson Creek; drawing down the lake for treatment of rough fish (carp) with the chemical rotenone; and application of aluminum sulphate on the lake bottom to reduce nutrient exchange between lake sediments and lake water. The plan also included reducing nutrient and sediment loads through wetland restoration and creation. About 125 acres of existing wetland and farmed wetlands at the confluence of Jackson Creek and its major tributary were selected for restoration/creation (Helsel and MacKinnon 1995). An 85-acre wetland was constructed to reduce sediment and nutrients entering the lake. This Lake Renewal Plan, funded by U.S. EPA's Clean Lakes Program, was implemented in coordination with the activities funded under the Turtle Creek Priority Watershed Project.

Rock River Water Quality Management Plan, Lower Rock River Appendix. WT-668-2002. South Central Region, WDNR.

Date  2002

Author   Aquatic Biologist

Historical Description

A large natural lake managed for largemouth bass, pan fish, and walleye. Major management problems are carp and pollution. Rough fish removal has since both state and town roads border the pond. Only one farm has frontage and there are no recreational facilities.

Surface Acres = 2,072, S.D.F. - 2.77, Maximum Depth = 56 feet.Source: 1961, Surface Water Resources of Walworth County,WI: WI-DNR Delavan Lake, T-2-N, R-16-E,

Date  1961

Author   Aquatic Biologist

General Condition

Delavan Lake House In The Wood Beach was assessed for the 2018 listing cycle; E. coli data sample data were clearly below the 2018 WisCALM listing thresholds for the Recreation use. This water was meeting its designated uses and not considered impaired.

Date  2017

Author  Ashley Beranek

Impaired Waters

Delavan Lake (WBIC 793600) was placed on the impaired waters list for total phosphorus and excess algal growth in 2016. The 2018 assessments showed continued excess algal growth; new chlorophyll-a sample data exceeded the 2018 WisCALM listing thresholds for the Recreation use. Total phosphorus data were clearly below the Recreation use and Fish and Aquatic Life use listing thresholds. Based on the most updated information and biologist input, no change in the existing impaired waters listing was needed.

Date  2017

Author  Ashley Beranek

Impaired Waters

Delavan Lake (WBIC 793600) was assessed during the 2016 listing cycle; chlorophyll sample data exceed 2016 WisCALM listing thresholds for the Recreation use, however, total phosphorus data do not exceed REC thresholds. Total phosphorus and chlorophyll data do not exceed Fish and Aquatic Life thresholds.

Date  2015

Author  Aaron Larson

Condition

Wisconsin has over 84,000 miles of streams, 15,000 lakes and milllions of acres of wetlands. Assessing the condition of this vast amount of water is challenging. The state's water monitoring program uses a media-based, cross-program approach to analyze water condition. An updated monitoring strategy (2015-2020) is now available. Compliance with Clean Water Act fishable, swimmable standards are located in the Executive Summary of Water Condition in 2018. See also the 'monitoring and projects' tab.

Reports

Recommendations

Management Goals

Wisconsin's Water Quality Standards provide qualitative and quantitative goals for waters that are protective of Fishable, Swimmable conditions [Learn more]. Waters that do not meet water quality standards are considered impaired and restoration actions are planned and carried out until the water is once again fishable and swimmable

Management goals can include creation or implementation of a Total Maximum Daily Load analysis, a Nine Key Element Plan, or other restoration work, education and outreach and more. If specific recommendations exist for this water, they will be displayed below online.

Monitoring

Monitoring the condition of a river, stream, or lake includes gathering physical, chemical, biological, and habitat data. Comprehensive studies often gather all these parameters in great detail, while lighter assessment events will involve sampling physical, chemical and biological data such as macroinvertebrates. Aquatic macroinvertebrates and fish communities integrate watershed or catchment condition, providing great insight into overall ecosystem health. Chemical and habitat parameters tell researchers more about human induced problems including contaminated runoff, point source dischargers, or habitat issues that foster or limit the potential of aquatic communities to thrive in a given area. Wisconsin's Water Monitoring Strategy was recenty updated.

Grants and Management Projects

Monitoring Projects

Watershed Characteristics

Delavan Lake is located in the Turtle Creek watershed which is 288.47 mi². Land use in the watershed is primarily agricultural (69.80%), grassland (9.10%) and a mix of forest (6.50%) and other uses (14.50%). This watershed has 339.80 stream miles, 590.58 lake acres and 6,590.97 wetland acres.

Nonpoint Source Characteristics

This watershed is ranked Not Available for runoff impacts on streams, Not Available for runoff impacts on lakes and High for runoff impacts on groundwater and therefore has an overall rank of High. This value can be used in ranking the watershed or individual waterbodies for grant funding under state and county programs.However, all waters are affected by diffuse pollutant sources regardless of initial water quality. Applications for specific runoff projects under state or county grant programs may be pursued. For more information, go to surface water program grants.