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cause for concern provided that early spring (pre-snowmelt) water levels have not exceeded 870.7 feet. And despite the scarcity of existing lake Level data, it appears that the lake rarely, if ever, reaches 870.7 feet. As a management strategy, EIevation 870.5 has been established as a management "action" Level for Twin Lake. It should be noted, however, that this analysis assumes both the continued absence of inflow from Vadnais Lake; and a continuation of the existing hydrologic regime for the Iake. If the projected 63 cfs inflow from Vadnais Lake were actually permitted into Twin Lake, storage capability would be exhausted in Iess than 3 days and the lake would rise above the 875-foot elevation limit. 5.2 Water OuaIity Twin Lake's unusual hydrologic situation has allowed it to remain relatively free of pollutants and algal overabundance. Changes in the lake's watershed are likely to result in changes in the lake's water quality. Preservation of the current water quality conditions in Twin Lake will require management of possible sources of nutrients or contamination. Twin Lake is currently segregated from the drainage system for the nearby Interstate highway. This segregation is desirable, since it prevents pollutants in the highway stormwater runoff -grease and oil, particulate matter, roadside debris, etc. -from reaching the lake. If possible, this segregation should be maintained. According to personnel at the SPWU, Eurasian water milfoil has been found in Vadnais Lake. As a result, the current practice of the SPWU is to maintain lake levels below the outlet, thus preventing flow from Vadnais into Twin Lake. In addition to the exotic species problem, other consequences of receiving flow from Vadnais must be considered. Vadnais is positioned at the downstream end of a very Iazge watershed, and therefore is subject to much Iarger loading rates of contaminants and fertilizers than is Twin Lake. If Twin Lake is to be isolated from. nutrients from the larger watershed, the segregation between the Lakes should be maintained. IVew construction within the watershed can contribute an increased silt and sediment load to the Lake. Establishing and maintaining effective erosion control measures during and.after any periods of construction will be necessary. Construction will. also bring an increase in the amount of impervious surfaces (such as roofs, roads, driveways) and stormwater conveyances. These will contribute increased amounts of organic material and increased stormwater runoff rich in nutrients expected to cause an increase in algal production. Landscape and stormwater system design measures to mitigate these effects 23162\264\TWINLAKE.RPT\I~VIIi 9