Twenty-eight million Americans and eight million Canadians live around these lakes. The Great Lakes Basin includes twenty-eight cities with populations over 50,000 and are supported by more than 13,000 manufacturing and industrial plants. Millions of gallons of Great Lakes water are used daily for drinking, recreation, transportation and industrial processes. In the Great Lakes themselves, the tributaries that flow into them, and in fact in many of the inland lakes, streams, and rivers in the United States, toxic contamination of fish has taken place. This has restricted the use of many of these fisheries, causing large economic losses to the country's sport and commercial fishing industries.
Toxic substances enter the nation's water system via a number of pathways.
Some sources include industrial waste discharges, effluent from sewage treatment plants and waste disposal sites. These are subject to varying degrees of government regulation. Other sources of contaminants include land runoff and the atmosphere. They expose higher vertebrates, including humans, to some contamination. These compounds accumulate and increase in concentration higher up the food chain.