Watershed District Grades Lake Minnetonka's Water Quality

The water quality of most Lake Minnetonka bays has dropped a notch in the last year, according to data released yesterday by the Minnehaha Creek Watershed District, but remains generally good or better in most areas.

While 13 of Lake Minnetonka's 29 bays received a grade of "B" or better, 18 bays received a lower mark that they did a year ago. Grays Bay was the only Lake Minnetonka bay to improve its grade, going from an A- in 2011 to an A in the most recent report card. Lower Lake North and Wayzata Bay were the only other bays to receive an "A"—although Carsons Bay, Gideon Bay, Lafayette Bay, Lower Lake South, St. Albans Bay and Spring Park Bay all received an "A-."

Because they are able to absorb higher levels of contaminants, bays with deeper water consistently receive higher grades that shallow areas.

Tanager Lake, Jennings Bay and Halstead Bay received the lowest marks, with all three being graded a "D."

The Minnehaha Creek Watershed District takes water samples from May to September and bases its lake grades on three water quality parameters: water clarity (Secchi disk depth), algae growth (Chlorophyll-a ) and nutrients (total phosphorous). Factors such as aquatic plants, fisheries, harmful chemicals and over-use can also affect a bay's grade.

The Minnehaha Creek Watershed District’s lake grading method was developed in 1989. The grade shows how a lake or bay measures up compared to other area waters. Grades are an indicator of the perceived condition of the open water.

“The information we collect each year helps the District determine which water quality improvement projects to pursue,” said Eric Evenson, Minnehaha Creek Watershed District administrator. “The sound scientific data we have amassed provides a solid foundation for decision making.”

Evenson pointed to shoreline restoration projects that prevent erosion and filter runoff into Lake Minnetonka and an innovative sand/iron filter that removes dissolved phosphorous from a stream that feeds Dutch Lake as examples of recent water quality improvement projects the watershed district has implemented.

The Minnehaha Creek Watershed District also has a Cost Share Grant Program that helps fund the installation of raingardens, pervious pavers, shoreline plantings and other stormwater management techniques.

Pet waste, lawn clippings, fertilizer or other chemicals that reach Lake Minnetonka represent some of the biggest threats to local water quality. These and other contaminants typically enter the water via storm drains, going unfiltered into streams and tributaries.

The watershed district also offers the following recommendations to protect water quality:

• Residents can use rain barrels to control excess water flow into waterways, pick up pet waste, bag leaves and lawn clippings and reduce fertilizer use. 
• Boaters can protect lakes by observing the state law against transporting aquatic invasive species (AIS), including zebra mussels.
• Lakeshore property owners can help prevent the spread of AIS by only hiring certified lake service providers to install or remove water-related equipment (boats, docks, boat lifts or other structures). All hired providers that perform this work on Minnesota bodies of water are required by state law to undergo the training program. For more information, go to the AIS page on the Minnesota Department of Natural Resources website, www.dnr.state.mn.us/eco/invasives.

For more information on water quality of the district’s lakes and streams, visit the water quality section of Minnehaha Creek Watershed District’s website.

The Minnehaha Creek Watershed District covers approximately 181 square miles, including Minnehaha Creek, Lake Minnetonka, the Minneapolis Chain of Lakes and Minnehaha Falls. The district is charged by state law to protect, improve and manage water resources. It does so through scientific research and monitoring, public education, cost share grant programs, permitting and collaborative efforts with the 27 cities, two townships and two counties (Hennepin and Carver) that are in the District.