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The lake's extensive littoral (i.e., shallow) region and its good water clarity have resulted in a profuse weed growth throughout the shallow region of the lake. In previous years, weed harvesting during the late summer has been necessary to facilitate recreational use of the lake. The aquatic weed Eurasian Watermilfoil (Myriophyllum spicatum) was identified in Silver Lake for the first time in 1992. Its growth was noted in localized areas at about 20 different locations within the lake. This exotic plant has few natural enemies or controls. Its ability to regrow from small fragments and out -compete native aquatic plant species enables it to spread rapidly and to become a noxious weed. Dense growths of Eurasian Watermilfoil may result in habitat degradation, pose a hazard to navigation, and are an aesthetic nuisance. To eradicate growths of Eurasian Watermilfoil from Silver Lake, each area of growth was chemically treated with 2-4-D in 1992 and 1993. The treatment appears to have been successful. However, Ramsey County continues to survey the lake to evaluate the success of the eradication efforts. Weed harvesting in the lake was discontinued pending completion of a survey confirming that eradication was complete. 4.2.1.5 Public Use and Related Water Quality Concerns Silver Lake is a very intensively used lake in VBWD. Its intensive use is due primarily to the two parks located adjacent to the lake, A park on the south shore is owned by the city of North St. Paul and includes a public swimming beach and an extensive picnic area. A fishing pier, located within the park, was installed adjacent to the beach area in July of 1989. The park on the north end is owned by Ramsey County and contains three picnic areas and a public boat launch. The primary recreational uses of Silver Lake are swimming and fishing. A 1978 DNR recreational use survey estimated the lake supports fishing at the rate of 76 person -hours per acre, twice the regional average. The installation of a boat access in 1984 significantly increased fishing pressure. Other recreational uses include waterskiing, canoeing, and passive uses such show and ice cream social on the lake. Ramsey County indicates that the primary concern of lake users is the weed growth throughout the shallow region of the lake. The County believes current algal levels and water clarity are satisfactory to lake users. This observation is consistent with the results of MPCA surveys of citizen volunteers and MPCA staff members concerning the water quality a lake must have to fully support all types of recreational uses, including swimming. Such surveys indicate a lake's water quality must correspond to oligo-mesotrophic conditions to fully support swimmable and aesthetic uses (MPCA,1990). As mentioned previously, Silver Lake algal levels (i.e„ chlorophyll a) and water clarity (i.e., Secchi disc) are within the mesotrophic category. Based on survey results, the MPCA recommends that the Secchi transparency of a mesotrophic lake remain greater than 2 meters a majority of the time to avoid the perception of impaired swimming. As shown on Figure 4-2, the average Secchi transparency of Silver Lake has been greater than 2 meters during the past six years. In 1989, the City of North St. Paul surveyed residents as part of their water management planning process. Approximately one-third of the survey respondents identified concerns in the Silver Lake area. Survey results identified the following problems for Silver Lake, which are quoted from the North St. Paul Surface Water Management Plan: ■ Sedimentation at storm sewer inlets ■ High nutrient loading ■ Extensive in -lake vegetation f t, 23\82\045\SEC4.RPT\KMH 4 DRAFT: June 23, 1994