Half Moon Lake TMDL

Purpose

Half Moon Lake (Hydrologic Unit Code 070500006) is a small, shallow eutrophic lake that formed as an oxbow of the Chippewa River. The lake is geographically located within the City of Eau Claire and the Lower Chippewa River Basin. The lake is highly eutrophic and exhibits excessive algae and aquatic macrophyte growth (Borman, 1990; Brakke, 1995; Konkel and Borman, 1996; James et. al., 2001, 2002).

Objective

Half Moon Lake was originally listed on Wisconsin’s 303(d) impaired waters list in 1998 for eutrophic conditions and sedimentation and listed as a high priority for TMDL development on the October 2002 303(d) list. Half Moon Lake is 53 hectares (132 acres) in size with a maximum depth of about 3 meters (slightly over 9 feet). The lake’s watershed is 577 acres and approximately 85% of the shoreline is publicly owned by the City of Eau Claire. Land use in the watershed is 45% residential, 41% open land and 14% commercial (Barr Engineering, 1992). The City has a policy of purchasing properties abutting the lake when they become available and at the present time, only four privately owned properties remain along the shoreline.

Outcome

The lake is used extensively for recreation, especially boating and fishing. Although boating is allowed on the lake, no outboard motors are allowed with the exception of the Ski Sprites, a local water-ski club that uses the lake for practice and exhibition shows during the summer. The Ski Sprites use ski boats with high horsepower outboard motors for these activities. Because of its shallow depth, enriched sediments and excessive water column phosphorus levels, the lake experiences heavy macrophyte growth and severe algae blooms during the summer. These eutrophic conditions have significantly impaired body contact recreational activities.Historically, the lake frequently experienced winterkill conditions, but since the City installed aerators in 1979, adequate dissolved oxygen conditions have been maintained throughout the winter. Algae blooms in Half Moon Lake are often accompanied by excursions of the Wisconsin water quality criterion for pH. The elevated lake pH levels are due to removal of carbon dioxide from water during photosynthesis (by macrophytes and algae). The reduction in carbon dioxide levels during daylight causes an increase in pH. A reduction in phosphorus levels would result in a decrease in chlorophyll levels (a measure of productivity) and a reduction in maximum pH levels. The lake was placed on the Wisconsin 303(d) list in 1998 and 2002 due to eutrophication and pH exceedances above the 9.0 water quality standard. Lake sampling conducted by the Wisconsin Department of Natural Resources (WDNR) during the summers of 1997 and 2001 found pH levels above 9.0 on 4 of 4 (100%) of the summer sample dates when all sites are considered. In addition, bi-weekly monitoring conducted by the U.S. Corps of Engineers (USCOE) during summer 1999 found pH violations on 8 of 11 dates (73%).

QA Measures

Run Project Summary Report

TMDL/303d Projects
Implement TMDL
Half Moon Lake TMDL
2006
Active
 
Reports and Documents
Approved 8-30-2004.
Data Documentation
Phosphorus Total Maximum Daily Load (TMDL) for Half Moon Lake, Eau Claire, Wisconsin Wisconsin Department of Natural Resources September 25, 2008
Data Documentation Half Moon Lake Impaired Water Listing Documentation, Eau Claire County
 
Activities & Recommendations
TMDL (USEPA) Approved
Half Moon Lake was originally listed on Wisconsin's 303(d) impaired waters list in 1998 for eutrophic conditions and sedimentation and listed as a high priority for TMDL development on the October 2002 303(d) list. Half Moon Lake is 53 hectares (132 acres) in size with a maximum depth of about 3 meters (slightly over 9 feet).
 
Waters