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clarity indicates few algae are present in the water, and the lake is desirable for all types of recreational activities. However, algal growth throughout the summer causes the transparency to decline to one or two meters by late August each summer. The MPCA conducted surveys of citizen volunteers and MPCA staff members to determine the level of algal growth the public perceives as interfering with the enjoyment of swimming in a lake, The survey results indicate most people would associate transparencies of less than 1.5 meters as either "swimming impaired" or 'no swimming". Applying the MPCA survey results to the Lake Jane water quality data suggest that the algal blooms in Lake Jane during the late summer interfere with public enjoyment of the lake for swimming. The MPCA survey results indicate that Lake Jane's current water quality places it in a category of being undesirable for swimming activities during the late summer period. Based on the results of its surveys, the MPCA recommends that the Secchi disc transparency of a lake remain greater than two meters a majority of the time to avoid the perception of impaired swimming. As shown on Figures 4-14, Lake Jane's growing season Secchi transparency values have remained less than two meters during much of the late summer period, even during years when it was treated with an algicide. The MPCA has found that water transparency less than one meter and frequent algal blooms make a lake undesirable for boating and for any swimmable use (MPCA, 1990). During 1987 and 1988, the Secchi transparency values were less than one meter for a short period of time during August. The data indicate that late summer algal blooms occur in the lake annually, but the severity of the blooms vary from year to year. During 1987, 1988, and 1991, algal blooms during the late summer period were more severe than algal blooms noted during 1989, 1990, and 1992. The lake was treated with an algicide during 1989 and 1990, and the treatment may have reduced the severity of algal blooms. Although the lake was not treated with an algicide during 1992, reduced late summer algal blooms were noted. Algicide treatment of Lake Jane has not occurred since 1990. Historically, treatment ' occurred in 1976,1984, 1989-, amJ 1990-.-Discussions with lake residennus 1 dic`ate they agree that -- algal blooms during the late summer are undesirable and interfere with their enjoyment of swimming in the lake. However, not all of the residents agree about the need for algicide treatment of the lake. Some feel strongly that the lake should be treated. Others believe treatment is unnecessary. Therefore, no treatment has occurred since 1990. Historical total phosphorus, chlorophyll a, and Secchi disc transparency averages (see ° Figure 4-13) indicate the water quality of Lake Jane has varied somewhat from year to year. Results of a trend analysis of Lake Jane water quality data showed a significant decrease in } chlorophyll a, but no significant changes in total phosphorus, or transparency (Secchi disc) over the 1971 1990 period. A significant change in all three indicators is needed to indicate a significant change in water quality. j The Lake Jane water quality data indicate relatively good water quality in the lake during the entire period of record. The data indicate the lake's average growing season phosphorus concentration has consistently been within the moderate category. The long term average growing season total phosphorus concentration from the lake's epilimmon (0.028 mg/L) is very similar to the most recent summer average (0.025 mg/L in 1991). The data were compared to criteria used to denote a lake's nutrient "status" (NALMS, 1988). Based on this comparison, Lake Jane would be assigned a trophic status of mesotrophic. This simply means that the lake has a moderate amount of nutrients. As shown in Figure 4-13, the growing season average total phosphorus concentration has generally been within the mesotrophic category throughout the period of record (1971-1991). 23\82\045\SEC4.RPT\KMH 32 DRAFT: June 23, 1994