Water quality assessment of Lisgar Lake, Tillsonburg, Ontario

Lisgar Lake is a 6.8 ha hardwater lake with a maximum depth of 6.8 m. Centrally located in the town of Tillsonburg, it provides important aesthetic and recreational benefits to the public in a region where lakes of recreational size are rare. This report summarizes the water quality of Lisgar Lake during the ice-free season of 1987. Eutrophic Lisgar Lake experienced peak phytoplankton densities in late summer. Chlorophyll a levels were correlated to algal biovolumes and reached concentrations as high as 62 ?g/L, with an annual mean of 19.6 ?g/L. As the season progressed, the algal assemblage became increasingly dominated by blue-green algae which comprised 60 % of the total algal biovolume by late August. Water clarity, as measured by Secchi disc, varied from 4.0 m in the spring to less than 1.0 m by late summer. Mean annual TN:TP ratios were 173:1, but fell to less than 5:1 during the blue-green bloom episodes.