Simply Science: Minnehaha Creek Watershed District grades its lakes

MINNETONKA, Minn. - Just like students in school, the lakes in the Minnehaha Creek Watershed District are given a grade based on water quality. Grays Bay on Lake Minnetonka has been given an "A."

Kelly Dooley is a Water Quality Specialist for the Minnehaha Creek Watershed District. She explains, "We do routine water quality monitoring twice a month, from May to September. We look at nutrients, we look at algae and we look at water clarity."
Phosphorous and chlorophyll levels relate to the lake's algae content and are measured with a 2 meter composite tube.

Water Quality Assistant Kailey Kreatz demonstrates, "Instead of just doing a grab sample off the surface, we'll lower the tube into the water and that way we're getting an accurate sample of the whole 2 meter surface instead of just the very surface of the water."

Water clarity is measured with a secchi disk. "So we'll lower secchi disk and we just lower it until you can't see it anymore and we'll take note of how deep it is," continues Kreatz.
"The state standard is 1.4 meters for a deep lake so 1.6 is definitely a good reading for Grays Bay," she adds. Twenty other lakes within the watershed received an A grade.

Twenty-one were rated D or F, which wasn't a surprise considering that many of these are shallow or receive a high volume of storm water runoff, both contributors to poor water quality.

The Watershed District looks from year to year at the changes but a longer study, over years, is being conducted and those results are expected in July.
To view a list of all the District's lakes and their grades visit the report online at


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