4.4 Water Quality Issues

Lake Issues

The Hydrologic and Hydraulic and Pollutant Loading Study (HHPLS) through an extensive public participation process established water quality goals for 62 lakes and Lake Minnetonka bays in the District.  Eleven of those lakes and most of the bays currently meet, nearly meet, or exceed their water quality goal.  In addition, nine lakes in the watershed are listed on the Minnesota Pollution Control Agency's 303(d) list of Impaired Waters for excessive nutrient concentrations that impair full recreational use of the lake. 

According to monitoring data, the following resources do not currently meet state nutrient standards and may be in the future designated as impaired waters:

Dutch Lake Tanager Lake Lunsten Lake
Gleason Lake Mooney Lake Halsted Bay
Langdon Lake Stone Lake Jennings Bay
Long Lake Lake Auburn East West Arm

Stream Issues

The streams in the upper watershed convey significant phosphorus and sediment loads to Lake Minnetonka and other lakes and wetlands in the watershed.  In some of those streams, summer dissolved oxygen levels fall below the levels necessary to sustain aquatic life.

Impact of Future Development

Development and redevelopment on the watershed is expected to increase nutrient and sediment loads, continuing to further degrade water quality and ecological integrity in lakes, streams, and wetlands.

Lack of Data

Even with the extensive amount of study and analysis completed in the watershed and a significant annual hydrologic data collection program, much is still unknown about the water resources in the watershed.  In some lakes little or no data is available to assess water quality.  Lake Minnetonka is comprised of a series of interconnected bays that interact in complex ways.  A whole-lake model is needed to better understand the dynamic and complex relationship between the many bays and open-lake areas of Lake Minnetonka.

Shallow Lakes Issues

Many of the lakes in the watershed are shallow lakes or exhibit some shallow lake characteristics.  Shallow lakes are different than deep lakes.  Internal lake processes tend to be more important to their water quality than external sources such as pollutant loading from the lakeshed, and management strategies may differ.