A Canada-wide survey was undertaken of sites associated with coal mines and coal-fired electrical generating stations. Several water samples were found to contain very high concentrations of thallium, iron and manganese. High thallium concentrations were found in several sites in Eastern Canada, in spite of the greater coal consumption and production in the western and central regions. The data suggest that coal type (rather than quantity) and/or regional geological contributions are responsible for the high Tl concentrations observed. Our findings, coupled with others around the world, strongly indicate that Tl is an environmental pollutant. In sediments, the observed high ratios of Tl/Hg suggest there is an enrichment of Tl by at least 25% when compared to crustal concentration ratios.