2.3.2 Biologic Integrity

Landscape

The subwatershed is almost fully developed, and there are only a few remaining patches of relatively undeveloped landscape.  Most of these are wetlands or are wooded portions of large residential lots.   No areas within the subwatershed have been identified by the DNR or the Minnesota County Biological Survey (MCBS) as being high-value vegetative or ecological areas.   

Lake

The most recent DNR fish survey for Christmas Lake was conducted in 2001.  It identified a healthy sport fishery featuring rainbow trout and healthy panfish population consisting of bluegills and pumpkinseed and hybrid sunfish.   Northern pike, largemouth bass, green sunfish, and yellow perch were also found during the fish survey.  Christmas Lake is one of the few lakes in the Metro Region that is managed as a two-story (both cool and warm fishery) lake because of its good water quality. This means that the lake is cold enough and has enough oxygen to support trout at depths normally devoid of fish during the summer. To support the two-story fishery the lake continues to be stocked with catchable size adult rainbow trout. The Minnesota Natural Heritage Information System lists two fish species of special concern in the Christmas Lake subwatershed: least darters and pugnose shiners.

Christmas Lake 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 Christmas Lake.  Mercury contamination is being addressed by a region-wide TMDL process by the MPCA.

Eurasian watermilfoil has been confirmed in Christmas Lake since 1992.  The City of Chanhassen obtained an aquatic vegetation survey in 2001 from the firm Blue Water Science.  The survey revealed a wide variety of beneficial vegetation as well as Eurasian watermilfoil and curly leaf pondweed.  At that time the dominant species was water celery, a plant that is an important food for waterfowl and that provides good spawning habitat and cover for fish.  Other dominant species include northern watermilfoil, coontail, chara, and water stargrass.  Eurasian watermilfoil was found at about one-third of the sampled sites but was sparse and mixed with other native plants.  Curly leaf pondweed was found at about one-quarter of the sampled sites, but at low densities.

Wetlands

The 2003 MCWD Functional Assessment of Wetlands (FAW) identified one small wetland with exceptional vegetative diversity and another with high diversity.  Three wetlands were classified as having exceptional aesthetic and fish habitat values (see Figure 13).