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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: 3 [Category II] limits are 40 ug/L summer average chlorophyll and about 75 ug/L summer average total phosphorus. The corresponding summer average Secchi disc reading would be about 2.0 feet (0.6 meters). ...Lake depth is critical in predicting the tendency of a lake toward winterkill conditions when large numbers of fish perish due to low dissolved oxygen conditions during late winter...Lakes with greater mean depths have a greater volume of water in relation to their sediment surface area, hence a longei- time is needed to deplete the overlying water of dissolved oxygen. A study of several lakes in the Metropolitan Area which have game fish populations indicate that winterkill conditions are likely to occur periodically in eutrophic lakes having a mean depth of 13.3 feet (4 meters) or less. Lakes having a significant volume of winter inflow and outflow are normally less susceptible to winterkill than lakes with no continuous inflow and outflow. The GLWMO Category II classification matches up to the Valley Branch Watershed District classification except for the Secchi disc criteria (GLWMO's is 0.9 meters, whereas VBWD's is 0.6 meters). A summarized version of this description (or the entire description) can be added to the plan. The GLWMO Category III classification could be thought of as a "wildlife habitat and aesthetics" category, which in some cases may support warm water fishing if the lake is not subject to winterkill. Questions for the Board: 1. Should a "fishing" description be added to the Category II classification? 2. Should other changes be made to the lake and pond classification system? Lake Water Quality Goals At previous meetings, the Board discussed the possibility of setting "stretch" goals for the lakes. At the March 23rd meeting, Barr discussed the reason stretch goals were not set for the lakes (all feasible best management practices recommended in the diagnostic feasibility study were implemented, so not cost effective to do more than that at this time). One of the Board members suggested that a possible stretch goal would be alum treatment of lakes. The cun-ent draft of the GLWMO plan takes a "hands off 'attitude regarding aquatic plant management, leaving it to the local lake associations and cities. The GLWMO may wish to add a policy to the GLWMO plan that reflects the possible role of aquatic plants in lake water quality (especially in shallower lakes). Ban-'s future conditions analysis shows that the projected future water clarity (Secchi disc) conditions for Lake Owasso, Lake Wabasso, and Snail Lake will not be as good as current conditions. We have also