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• The inorganic nitrogen concentrations (NO3-N + NH4-N) in the surface waters during the summer varied between 30 and 120 ugil with lowest concentrations occurring during mid-June and late August in 1976. These concentrations should not produce excessive algae blooms during the summer months. However, spring concentrations of total phosphorus are quite high and are indicative of eutrophic conditions. The chlorophyll a concentrations throughout the summer months were low (Figure B-22) , with correspondingly good water transparency. No algae blooms occurred at the surface during summer months. Stauffer (1974) monitored Fish Lake in 1972 and provided data indicating similar low surface chlorophyll concentrations, but also a summer chlorophyll maximum of about 20 ugh occurring at about 10 meters in depth. This condition is often the result of Oscillatoria rubescens, a cold-water blue-green filamentous algae that is found near the lake surface during spring and fall and in the lower metalimnion during the summer, if light penetration is sufficient through the epilimnion. Oscillatoria sp. was confirmed in the surface plankton of Fish Lake during the spring and fall of 1976 and 1977, when chlorophyll concentrations were rela- tively high, but not during the summer months when chlorophyll concen- trations were low. This may explain the relatively high concentrations of total phosphorus found during spring turnover which did not result in any excessive summer phytoplankton growth in surface waters. A comparison between the phosphorus data collected by Stauffer (1974) in 1972 and the monitoring data collected in 1976 and 1977 indicated an increase in summer concentrations of total phosphorus in both the epilimnion and hypolimnion. All of the 1972 data had surface concentra- tions of total phosphorus no greater than 20 ug/1 whereas the 1976 and 1977 monitoring data had concentrations ranging between 20 and 50 u9/1 as previously mentioned. Although Stauffer did not always sample at the deepest location in the lake, generally his hypolimnetic phosphorus concentrations were less than 60 ugh] throughout the entire summer period, even though his dissolved oxygen concentrations were near extinction. The 1976 and 1977 monitoring data indicated hypolimnetic phosphorus concentrations to be as much as 200 ug/1 or higher. High concentrations of phosphorus in the hypolimnion are the result of phosphorus (dissolved reactive) coming into solution from anaerobic lake sediments rich in phosphorus . The concentrations of phosphorus in Fish Lake during 1976 and 1977 were not as high as concentrations found in other eutrophic lakes, or lakes Mendota or Monona, but are sufficiently higher than the 1972 data to warrant concern about the increase in phosphorus availability within Fish Lake. A detailed study should be initiated on Fish Lake to assess the role of the mobile home park septic systems on this apparent increase in lake phosphorus concentrations. Fish Lake has the best water quality of any lake in Dane County, and therefore, prevention of any further degradation is warranted. Fish Lake has the potential to support some cold-water fish such as cisco; however, pollutants must be reduced and summer dissolved oxygen conditions must be improved if the lake is to continue to support any cold-water fish. B-103