3.4.1 Water Quality

The District’s Hydrologic Data Program monitors and collects data on water quality in many of the lakes and streams in the watershed.  Each year about 25 lakes are monitored, and 20-25 bays of Lake Minnetonka.  Some lakes have been monitored for a sufficient period of time that water quality trends can be determined.  For some of the lakes, however, insufficient data are available to draw statistically significant conclusions, and continued monitoring is necessary to better understand lake conditions.

Water quality grab samples are collected at eight locations on Minnehaha Creek, and at 15 locations on 10 Lake Minnetonka tributaries in the Upper Watershed.  Automated flow records and flow weighted samples are collected at 3 locations on Minnehaha Creek and at several locations in the Upper Watershed.  Data for both lakes and streams is compiled on annual Report Cards that present water quality and quantity data in a highly readable format for the general public.  Detailed data is published in an Annual Hydrodata report.

The HHPLS included extensive pollutant loading and water quality modeling for major water resources in the watershed for both year 2000 and 2020 projected conditions, and serves as the basis for this Plan.

In 2005-2006, MCWD conducted an assessment of lake sediment cores to determine relative historical levels of nutrients within several lakes within the watershed including Carsons Bay, Gleason Lake, Halsteds Bay, Jennings Bay, Langdon Lake, Parley Lake, Spring Park Bay, St. Albans Bay, Stubbs Bay, and Wasserman Lake.  At the time of writing of this plan, only preliminary results of the study were available.  Analysis of the diatom testing shows that with the exception of Langdon Lake and Gleason Lake (with greater historic clarity), water quality goals identified by the regional teams through the HHPLS process are generally consistent with the historic attainability of the lakes evaluated.  Diatom testing and paleoecology will be used further to both assess additional lakes and inform the Impaired Waters evaluations throughout the watershed.