Abstract

Both Lake Ontario and Erie have experienced increasing outbreaks of toxic cyanobacteria. These organisms can produce a family of hepatotoxic peptides called microcystins. To investigate the occurrence of these toxins in the Lake Ontario ecosystem, more than 650 samples were collected between 2001 and 2005 from both off-shore and near-shore embayments and analyzed for cyanobacterial toxicity using a combination of chemical and molecular approaches. Microcystin toxicity was common in Lake Ontario and detected in about 10% of the samples tested, especially in the eastern end of the lake near Oswego Harbor and in the Bay of Quinte region. Offshore blooms where also detected and may be transported onshore by lake circulation patterns. Microcystin toxicity exceeded the WHO advisory limit of 1 ug/L in approximately 1% of the samples tested; however these samples were often located nearer shore where users of the lake were likely to come in contact with the toxic algae. Molecular analysis indicated that potentially toxic species were widespread in the New York embayments of this lake and may also act as a source of toxigenic organisms to the open water systems. The presence of both toxic and potential toxic cyanobacteria in this lake has an increasing impact on the end use of this valuable resource.