2006 Results
In 2006 Coon Lake had average water quality for this region of the state (NCHF Ecoregion), receiving an overall C grade. While 2006 was similar to most years back to 1980 when monitoring began, it was poorer than other years since 1994, except for 2001. The lake is slightly eutrophic. From late July through August the water was olive green colored; these were the times with the highest algae and phosphorus. ACD staff’s subjective observations were that “some” algae was present until August, when algae concentration increased. Subjective observation of recreational suitability was that recreation was minimally impaired until July, when swimming became slightly or moderately impaired.
Trend Analysis
Twelve years of water quality data have been collected by the Metropolitan Council (1980, ’84, ’94, ’97), the Minnesota Pollution Control Agency (1989), and the Anoka Conservation District (1998-2002, ’04, ‘06). When the data was last analyzed after 2004, there was a trend of significantly improving water quality from 1980 to 2004 (repeated measures MANOVA with response variables TP, Cl-a, and Secchi depth, F2,8=4.61, p=0.047). Most of those improvements occurred between the late 1989 and 1994 when no monitoring occurred. When 2006 data is included in the analysis, the trend is no longer statistically significant (F2,9=2.49, p=0.14). This is because 2006 water quality was poorer than all of the last eight monitored years (since 1994) except for 2001.
Discussion
The primary threats to Coon Lake include EWM, poor lakeshore management by property owners, and failing lakeshore septic systems. ACD staff noticed a high abundance of EWM fragments in the water on several occasions, probably partly from boat propellers fragmenting plants and partly due to homeowners physically clearing near-shore vegetation. Each fragment can grow into a new plant and begin new infestation centers. Residents can best prevent the spread of EWM by not disturbing or removing the abundant native plants. Residents should also increase the use of shoreline practices that improve water quality and lake health, such as native vegetation buffers and rain gardens. On a community level, correcting problem septic systems, perhaps by adding municipal sewer services, would likely be beneficial to the lake.