Measurable concentrations of heavy metals occur in all our lakes and are derived from both natural and human sources.

Of particular concern are fairly high levels of mercury in fish (a topic on which we have conducted a whole-lake research project) which is a common occurrence in unproductive lakes in northern and eastern Canada.

Much of this mercury (approximately 50%) is estimated to have been derived from human activities, especially the burning of coal. Most of the mercury travels in the atmosphere and is deposited on lakes and their surrounding watershed in rain and the sources may come from as far away as the Midwest USA or even Asia.