Twin Cities Lake Water Quality

It’s springtime again!  That means the Minnehaha Creek Watershed District’s (MCWD) lake monitoring program has resumed.  This program measures water quality in district lakes, then summarizes the data with a grade for each the lake.  A recent press release from MCWD announces that 2007’s lake water grades have been made public. Even though rainfall was below normal last year between the months of April and July, the water quality grades held steady for the most part with some minor changes in water quality from 2006 to 2007.  Usually, hot, dry weather leads to an increase in algae growth.  The unprecedented rainfall during the months of August and September may have balanced overall water quality.

During the 2008 season, MCWD’s water quality staff will continue collecting water quality data for 34 lakes and 12 streams in the watershed.  There will also be water depth measurements at 10 stream monitoring sites.  Additionally, a comprehensive scan of Lake Minnetonka’s water depth will be recorded for the creation of a detailed map of the underwater contours of the lake. The most recent publicly available map of this sort was created in 1957.

To calculate lake grades, MCWD’s water quality monitoring staff measure water clarity, nutrient levels, and algae growth throughout the open water season.  Those results are averaged into a numerical score which is translated into a lake grade between A and F.

Lakes are graded on a curve; the C grade means that a lake is typical for lakes in the seven-county Twin Cities metropolitan area.  C lakes may not be ideal for swimming, boating, and fishing due to summer algae growth. Lakes in the A grade range have clear water and are suitable for recreational activities. B-quality lakes are considered good for recreational use but may suffer from algae growth later in the season.  Lakes stamped with an F have severe algae problems and aren’t recommended for recreational use at all. To see what lakes MCWD has evaluated and their grades, the report card can be located here.

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