Some effects of shoreline cottage development on lake bacteriological water quality

Eighteen cottaged lakes and one uncottaged lake in Southern Ontario, and their inflowing streams were surveyed for bacterial indicators of pollution by membrane filter techniques. Water samples were taken on 5 consecutive days in the spring, summer, and fall of the year. Inputs of fecal indicator bacteria were determined through an analysis of variance. Fecal coliform and fecal streptococcus levels in lakewater varied in a seemingly erratic manner. When the bacterial densities at different points on the lake were examined by an analysis of variance, the locations with significantly higher densities of fecal coliforms and fecal streptococci were most often found along the cottaged shoreline. Total coliform densities did not show this relationship with the cottaged shoreline. In addition, after rainfall, a large increase in numbers of fecal coliforms were found in the cottaged lakes but not in the uncottaged lake. These findings indicated that the cottaged shoreline was a greater source of fecal indicator bacteria than the uncottaged shoreline. However, the highest concentrations of fecal indicator bacteria in these lakes were found in the inflowing streams. The bacteria in these streams arose from stormwater from undeveloped forested watersheds and were probably, therefore, of soil or animal origin.