Mercury is the most common contaminant in fish in the USA and Canada. 42 states have advisories against fish consumption due to high mercury levels, and unacceptable fish mercury concentrations exist in all Canadian provinces and the Northwest Territories, including remote "pristine" lakes. Mercury is a neurotoxin, which is a particular concern for prenatal life and infants, for whom safe levels of mercury exposure are lower than in adults. Concern also exists regarding the toxic effects of mercury on reproduction, behavior and survival in fish-consuming birds and marine mammals.

The Maine Bureau of Health currently advises people to restrict consumption of fresh water fish due to mercury, a highly toxic pollutant which poses significant risks to human health and wildlife. Studies have documented that Maine’s loons currently are being adversely affected by mercury contamination. The Legislature enacted a law establishing standards for allowable mercury pollution in Maine’s waters in order to protect human health. This law will help ensure that businesses and wastewater treatment plants continue to reduce mercury discharges into Maine’s waters.