A comparative study of eight Finger Lakes in central and western New York State, Honeoye, Canandaigua, Keuka, Seneca, Cayuga, Owasco, Skaneateles, and Otisco, revealed a strong correlation of water quality to the percentage of agricultural land in the watershed and varying rates of change in water quality over a four year period. The eight lakes were sampled monthly from May through October since 2005 with Otisco added in 2008. Surface and bottom water samples were collected at a minimum of two, deep-water sites in each lake, with additional sites in Owasco, Seneca and Cayuga. The samples were analyzed in the laboratory for total phosphorous (TP), soluble reactive phosphate (SRP), dissolved silica (SRSi), nitrates, chlorophyll-a, total suspended solids (TSS), and major ion concentrations following standard limnological techniques. CTD profiles of conductivity, depth, temperature, pH, dissolved oxygen, photosynthetically active radiation, fluorescence and turbidity were also collected at each site, as well as secchi disk depths, plankton, and titrations for dissolved oxygen and alkalinity. Water quality rankings were assigned to each lake by comparing annual averages of dissolved nitrates, dissolved phosphorous, total phosphates, chlorophyll a, total suspended sediments and secchi disk depths resulting in a separate ranking for each year and each lake in the study.
The percent of agricultural land in each watershed correlates more strongly to water quality than the size of or population in each watershed. Seneca Lake has gradually but steadily declined in water quality over the past four years, suggesting that nutrient loading is a critical problem in this watershed. Keuka, Skaneateles, Owasco, and to a lesser extent Canandaigua and Cayuga remained constant or improved slightly, most likely due to more stringent enforcement of water quality legislation in these watersheds. In 2007, water quality improved in Skaneateles and Owasco Lakes. At Owasco Lake, this observed improvement in water quality has been attributed to less rainfall delivering fewer nutrients to the lake. The impact was not as apparent in the other lakes because the water residence time is significantly longer in the other Finger Lakes. In Honeoye, internal nutrient loading from the anoxic and nutrient-rich sediments probably caused different responses.