The Hudson River is one of the nastiest waterways in the country, and in 1984 a vast 200-mile stretch of the river, from Hudson Falls to New York City, was declared a Superfund site. Due to the broad expanse of this territory, the river has been called America's largest Superfund site.
The river's biggest area of concern is the PCBs, or polychlorinated biphenyl, present in its waters, dumped there by manufacturing facilities on the Upper Hudson run by General Electric from 1947 to 1977. The PCBs have been shown to cause extensive contamination of fish, enough to cause rapid evolutionary change in some species. Humans can become contaminated from PCBs from mere water contact, via absorption through the skin, and contamination has been linked to everything from lower IQ to cancer.
The cleanup effort under way for the Hudson is the most aggressive environmental effort ever proposed to clean up a river, and will cost General Electric about $460 million to complete. To date, more than 1.3 million cubic yards of sediment have been removed, but much more work still lies ahead.