While Casco Bay may look pristine, toxic pollution is present in its waters, in its sediments, and in the tissues of its living organisms, including clams, fish, birds and marine mammals.  Toxics like heavy metals and organic contaminants can pose a threat to the health of aquatic life and humans.

How do toxins end up in Casco Bay?

Historic industries around Casco Bay -- including shipyards, tanneries and textile factories -- have left a legacy of toxic chemicals in the Bay's sediment and waters.  Today, nonpoint source pollution in the form of contaminated stormwater is the major contributor of toxic chemicals to the Bay.  Pollutants are also deposited from the air via local and distance sources, in the form of rain or dust.

Effects and status of toxic contamination in the Bay

Toxic organic chemicals and some metals can increase in concentration as they move up the food chain.  Those chemicals have the potential to disrupt the normal activity of hormones in mammals (including humans), causing cancer, adverse reproductive effects, birth and developmental problems, and effects on immune systems.

Studies have shown that mercury levels in Maine's fish, loons, and eagles are among the highest in the country.  Levels of this and other contaminants have led Maine to issue advisories and guidelines on safe fish and lobster consumption practices.

Despite evidence that toxic chemicals are found throughout Casco Bay and its watershed, there is some good news.  The levels of mercury, PCBs, dioxins, and many pesticides entering the environment have declined greatly over the past two decades.  Levels of most heavy metals, pesticides, tributyltin, PCBs and low molecular weight PAHs have decreased in the sediments of the Bay since 1991.