2.3.2 Biologic Integrity

Landscape

Several areas of undisturbed or minimally disturbed forest and wetland in the subwatershed have been designated Regionally Significant Ecological Areas by the DNR (see Figure 6), including areas abutting Classen Creek; the French Marsh area; a large wetland north of Stubbs Bay; and portions of Big Island.   The Minnesota County Biological Survey (MCBS) identified one area of high biodiversity significance and a few areas of moderate significance, mainly patches of maple-basswood forest.

The Minnesota Natural Heritage Information System lists several rare natural features in this subwatershed.  These include the state-listed threatened species trumpeter swan and Blanding’s turtle; and the state species of special concern: cerulean warbler, red-shouldered hawk, Acadian flycatcher, pugnose shiner, least darter, and American ginseng.  An additional species that is currently not on those protected lists but which is being assessed for inclusion, the fox snake, has also been documented in this subwatershed.

Lakes

The watershed is dominated by Lake Minnetonka, known as one of the premiere sport fisheries in the state.  The Minnesota DNR regularly surveys the fish community in the lake.   Fish surveys were conducted in 1992 on Libbs Lake and Forest Lake, and found that both were panfisheries dominated by bluegill.

Table 1.  DNR fish survey data.

Lake 

Survey Year

Fishery

Dominant Fish

Minnetonka

1997

2003

Sport - walleye

Bluegill, walleye, northern pike, yellow perch, bass, black crappie.  Stocked with muskellunge and walleye

Libbs

1992

Panfish

Bluegill, black crappie

Forest

1992

Panfish

Bluegill, white crappie, yellow bullhead

The Lake Minnetonka Conservation District regularly harvests the Eurasian watermilfoil that grows densely in several bays and channels and inhibits boat traffic.  No comprehensive aquatic vegetation survey data is available for Lake Minnetonka or the other lakes in the subwatershed.

Lake Minnetonka is under a Fish Consumption Advisory for mercury, and was added to the state’s list of Impaired Waters in 1998 for that reason.  The Minnesota Department of Health, Minnesota Pollution Control Agency (MPCA), and the DNR have collaborated to monitor fish for contaminants at over 1,000 sites in Minnesota.  Fish from popular lakes and streams and those from known or suspected polluted sites are routinely collected and tested for mercury, which is found in most fish tested in Minnesota lakes, and PCB contamination.  These test results are used to monitor pollution and to provide more specific fish consumption advisories beyond the general advisories for Minnesota.  More detailed fish consumption advice that is similar to or slightly more restrictive than the general advice has been prepared for Lake Minnetonka.  Mercury contamination is being addressed by a region-wide TMDL process by the MPCA.

Streams

Biological sampling on Classen Creek was conducted as a part of the Upper Watershed Stream Assessment.  Two sites were sampled; only one yielded more than the 100 organisms typically needed to assure a statistically valid score.  The F-IBI – an Index of Biotic Integrity identified to the organism’s family level – for one of the sites fell into the “Good” category, suggesting good water quality, whereas just downstream the F-IBI fell into the “Fairly Poor” category.  However, the F-IBI does not allow discrimination between low scores due to poor water quality or low scores due to lack of habitat.  The site scoring “Good” yielded the best correlation between habitat quality and macroinvertebrate diversity of all the sites samples as part of the Assessment.  Pollution intolerant species were sampled at this site, and there was a good diversity of species.  However, just downstream of that sampling site was one of the worst-scoring sites, yielding no macroinvertebrates and only a few gastropods.  While there was some difference in the quality of habitat, based on upstream sampling the site should have been expected to yield more organisms.   Additional sampling would be necessary to further explore this discrepancy and to adequately characterize the biological integrity of Classen Creek.

Wetlands

While there are some wetlands in the lake direct drainage area, most of the wetlands in the subwatershed are located in one of the minor subwatersheds that ring the direct drainage area.  A number of them were identified in the 2003 MCWD Functional Assessment of Wetlands (FAW) as having exceptional to high vegetative diversity and wildlife habitat potential as well as having high aesthetic values.   Several large complexes, including Classen Marsh, French Marsh, and Ferndale Marsh provide high-quality fish and wildlife habitat (see Figure 13).