Minnehaha Creek Watershed District Issues 2010 Lake Grades

Water Quality Held Steady Compared to Previous Years

As Minnesotans prepare for the fishing opener on Saturday, they have new information about the quality of the lakes they’ll be using this season. The Minnehaha Creek Watershed District (MCWD) has issued its 2010 report card on the health of district lakes and it finds water quality has held steady compared to previous years (see attached list).

We’re very fortunate to have such consistent water quality in the district,” said Kelly Dooley, MCWD Lakes Water Quality Technician. “Although there are often slight variations in a lake’s grade from year to year, these fluctuations are within the normal range we’ve seen recently.”

The MCWD takes water samples from May to September and bases its lake grades on three water quality parameters:

Secchi disk depth (water clarity)
Chlorophyll-a concentrations (algae growth)
Total phosphorous (nutrients)
The numerical score for each water quality parameter is then averaged to compute a lake grade on a curved scale from A to F.

  • Lakes with an A grade are generally healthy and characterized by beautiful clear water. These lakes are well-suited for recreational activities of all kinds throughout the summer. A total of 21 lakes received an A grade in 2010 (including A-).
  • Lakes with a B grade are also good for swimming and recreation, but late summer algae blooms may cut the season short. Four bays on Lake Minnetonka and 4 other lakes in the watershed earned a B grade in 2010 (including B+ or B-).
  • The C grade signifies that a lake is typical of lakes in the seven-county metropolitan area. C lakes may not be ideal for swimming, boating, and fishing due to summer algae growth. A total of 25 lakes received a C grade in 2010 (including C+ or C-).
  • When a lake gets a D or F, it has limited water transparency, severe algae problems and very limited recreational use. A total of 9 lakes received a D grade in 2010 (including D+ and D-) and only one lake received an F.

“Lake grades should not be considered an indication of water quality trends,” said Dooley. “They are used to describe general water quality characteristics compared to similar lakes in the Twin Cities metro area.”

Among the factors affecting a lake’s grade is the weather. There was a 12 percent increase in average rainfall in 2010. Above average precipitation can often result in more runoff that can carry pollution to our lakes and streams.

There are measures people can take to help improve their local lake’s grade. They can take advantage of MCWD cost share grant programs which help fund the installation of rain gardens, pervious pavers and shoreline plantings that prevent runoff from carrying nutrients and pollutants into our streams and lakes. They also can use rain barrels, 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 including zebra mussels. For more information, go to the AIS page on the Minnesota Department of Natural Resources website, www.dnr.state.mn.us/invasives/index.html.

View Lake Grades

For more information on water quality of the district’s lakes and streams, visit the water quality section of MCWD’s website, www.minnehahacreek.org.

Minnehaha Creek Watershed District

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. For more information, visit www.minnehahacreek.org.

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