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To: GLWMO Board and Staff From: Karen Chandler Subject: Discussion Topics for May 4°i Board Meeting Date: April 26, 2000 Page: 2 3. The Executive Summary includes the water bodies that are considered "WMO-managed," plus provides some information about other water bodies. An earlier question by the Board needs to be answered: should the scope of the water bodies classified by the Board be expanded (i.e. to include all DNR-protected water bodies)? What does it mean if the Board classifies additional water bodies - is there a difference between "WMO-classified" and "WMO managed"? Lake and Pond Classification System At the March 23`d meeting, the Board decided that the lake and pond classification system criteria should be revised slightly to match up better with the MPCA's lower limit for full support of swimming (Secchi disk of 1.6 meters). We revised Figures 7, 8, and 9 to reflect this change in the boundary between Category I and Category II. The text and tables in the plan will also be revised. The Board also requested more information about how the criteria were established for the categories, especially if there is some explanation besides swimming that can be given. Category I is the "swimming" category, which is probably the best understood and does not need more explanation. Category II could be considered the "fishing" category. The following description of a "fishing" category is excerpted from the Valley Branch Watershed District Water Management Plan (1995): Studies have shown that fish production increased predictably with increasing phosphorus levels. Fish production increases only up to an optimum point, however, and then begins to decrease due to a change in fish food supply, oxygen depletion and other effects of advanced eutrophication. Due to these conditions, the species composition will gradually change from game fish to a dominance of the so-called "rough fish" species such as carp. For a lake in which rough fish are not present the increased food supply due to advancing eutrophication can be utilized even further by the game fish, but an optimum level of production will still be reached as the detrimental effects of eutrophication act on the life cycles of the fish and fish food organisms. ...Studies on [warm water] fish production in ponds have indicated that total phosphorus concentrations in the range of 60 ug/L to 70 ug/L and chlorophyll [a] concentrations in the range of 38 [ug/L] to 55 [ug/L] were conducive for the production of bluegill sunfish (Hall, et al., 1970). Total phosphorus concentrations near 130 ug/L were well over the optimum level for warm water game fish production and ponds with these levels of total phosphorus favored the production of rough fish over game fish (Haines, 1973). Moyle (1954) indicated that total phosphorus concentrations near 50 ug/L were optimum for the production of largemouth bass and sunfish in Minnesota lakes. Data collected for a number of lakes in the Twin Cities...indicates that lakes with significant game fish populations had average total phosphorus concentrations ranging from 65 to 88 ug/L...Average chlorophyll [a] concentrations in these lakes ranged from 20 to 30 ug/L, with Secchi disc readings ranging from 4 feet (l .1 meters) to 5.5 feet (1.7 meters). Based on the above data, the recommended