06-25-1990 Council Packet - Laserfiche WebLink

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CHAPTER 4: Water Quality In-Iake resioraiion techniques arc largely experimental; their success in restoring degraded lakes is limited and uncertain. Several in-lake treatment methods have been tried in the metro area. The DNR has reponed some success with efforts to restore degraded lakes by removing rough fish and restocking with other species. It reports improved clarity and better fishing in those cases. Although limnologisis are learning more from each experiment, in-lake management techniques arc simply too poorly understood to be relied on for improving water quality at piesent. For example, calcium nitrate was injeaed into the sediments of Long Lake in New Brighton to prevent the release of pho^horous (the nutrient most closely associated with algal growth) from the sediments to the water. While the rate of phosphorous release from the sediments seemed to be reduced, lake water quality was unaffected by the treatment because the lake is so deep and phosphorus inputs from runoff greatly exceeded inputs from the sediments. The DNR, Metropolitan Council, watershed districts, water management organizations, and local governments all manage water quality to varying degrees (see Table 5.1 in Chapter 5). For example, the watershed districts. Metropolitan Council, and DNR all sample metropolitan lakes for various water quality parameters, but their sampling programs are r»ot coordinated. The Metropolitan Council focuses on factors that relate to recreational use. It tests about 120 lakes for nutrient levels, abundance of algae, water clarity, temperature, and oxygen content The watershed management organizations also snidy these factors. The DNR primarily samples lakes for factors related to fish habitat. EURASIAN WATER MILFOIL Eurasian water milfoil is a new and severe threat to Minnesota lakes. Eurasian water milfoil is a rapidly-growing, non-native aquatic weed that has recently been introduced to Minnesota lakes. The weed spreads when fragments break off and eventually take root in the sediments. Boat propellers often au up the weed and facilitate its spread. Because it is not native to this country, Eurasian water milfoil has no natural enemies to control its spread and can form dense mats on the water surface, restricting boating, swimming, and fishing. Eurasian water milfoil now infests portions of several lakes in the metro area and has reached the critical stage on Lake Minnetonka. In its early stages, the weed can be controlled or eradicated by aquatic herbicides. At advanced stages of irifestation, as in Lake Minnetonka, the weed can only be controlled by harvesting and cannot be eradicated. The Lake Minnetonka Conservation District (LMCD) began harvesting the weed this year. The spread of Eurasian water milfoil can only be prevented if people wash off their boats to keep fragments of the —ced from entenng new lakes. The DNR and some lake associations have bej n to post signs about the weed at lake access facilities, and volunteers now monitor boats leaving access sites on Lake Minnetonka. The Legislature has appropriated $250,000 to the DNR over the next two years for identification, monitoring, research, education, and control of Eurasian water milfoil. The Department of Natural Resources, Pollution Control Agency, and Department of Health work together to test fish caught in metro area lakes for the presence of PCBs and mercury. Where levels are high, a fish consuinption advisory is issued. No agency samples for chemicals sfleh as pesticides. Both the Metropolitan Council and Minnesota Pollution Control Agency maintain data centers with information on the water quality of metropolitan lakes. CONCLUSIONS Far less is knovm than is needed about the water quality of metropolitan lakes. Programs to monitor water quality in the metro area are limited ard uncoordinated. While several agencies monitor various aspects of water quality, they do not coordinate their activities very extensively. Some aspects of water quality arc not monitored at all.