Cedar Lake and McMahon Lake (locally known as Carl’s Lake) are located in Scott County. Excess phosphorus has limited their use and quality by causing frequent algae blooms and decreasing water clarity. A diagnostic study was conducted as part of a Clean Water Partnership project in the Sand Creek watershed.
Water quality data collected indicate that the lakes have not met state water quality standards over the past ten years of monitoring. The land use in the lakes’ watersheds is mainly agricultural with woodland areas and rural residential type of development. The predominant phosphorus sources for Cedar Lake are lake sediment release, carp, curlyleaf pondweed and watershed runoff. For McMahon Lake the primary sources are sediment release, curlyleaf pondweed and watershed runoff. Phosphorus reductions of 85 percent and 81 percent will be required for Cedar Lake and McMahon Lake, respectively, to meet state water quality standards. A separate implementation plan has been developed as part of a larger watershed project and identifies specific measures needed to achieve the desired reductions.
When lakes and rivers are polluted with phosphorus, sediment, and other contaminants, it can take years of effort and expense to restore water quality. But this restoration work is having an impact.
Map and location
Cedar Lake and McMahon Lake are located in the Minnesota River basin.
TMDL report and implementation plan
- Cedar Lake and McMahon (Carl’s) Lake Total Maximum Daily Load Report
- EPA Approval Letter (February 23, 2012)
- Cedar Lake and McMahon Lake TMDL Implementation Plan (June 18, 2012)
Eric Alms, Project Manager
Minnesota Pollution Control Agency
520 Lafayette Road St. Paul, MN 55155