The water quality of Seneca Lake has been studied since the early 1900's when secchi disk readings were first taken. At that time, the trophic state of Seneca Lake was classified as oligotrophic; that is, nutrient concentrations and primary production were low and transparency high. Water clarity remained approximately the same up through the early 1930s. In general, by the late 1970s water clarity had decreased, indicating the lake’s trophic status was mesotrophic. Total phosphorus concentrations from the 1970s were into the mesotrophic range. Chlolophyll-a concentrations also illustrate the trend toward more productive waters in Seneca Lake in the early to mid 1970s. Similarly in the early 1970s, the transparency of Seneca Lake had decreased to within the eutrophic range. These low transparency values were observed into the early 1990s. Based on the sampling done by the Seneca County Soil and Water Conservation District in the 1990s, an improvement in water quality of Seneca Lake is suggested – at least at the north end where the samples were taken. Summer total phosphorus levels have decreased and perhaps as a result, phytoplankton levels have decreased slightly as indicated by the decrease in chlorophyll levels. However, it should be noted that the increase in transparency and the decrease in phytoplankton levels may well be the result of the high filtering capacity of the invading zebra mussels into Seneca Lake. The monitoring data do not provide an answer to this question. The trophic status of Seneca Lake is currently best described as oligotrophic. In conclusion, water quality of Seneca Lake appears to have improved since the early 1970s and within the 1991-1998 period of monitoring by the Seneca County Soil and Water Conservation District.
Makarewicz, Joseph C.; Ward, Roger W. Jr.; and Lewis, Theodore W., "Water Quality of Seneca Lake 1991-1998" (1999). Technical Reports. 62.