New Bedford Harbor in Massachusetts is one of the most toxic bodies of water in the United States, yet it is home to a thriving population of killifish.

"You'd think nothing, absolutely nothing, would be able to live in New Bedford Harbor," Jim Kendall, president of New Bedford Seafood Consulting, told The Washington Post. "But you'd be dead wrong."

Killifish, 3-inch-long fish common along the Atlantic coast, are sometimes so thick "you could just about walk across on them," said Kendall. Exactly how the killifish survive is a mystery to scientists.

New Bedford Harbor was designated a Superfund site in 1983 by the Environmental Protection Agency, the Post reported. High levels of polychlorinated biphenyls were dumped into the harbor by factories from the 1940s through the 1970s and PCB levels are still far above what the EPA says is safe.

Killifish live for about three years, beginning to reproduce after one year. Since PCBs have polluted the harbor for tens of killifish generations, the fish have had a long time to adapt.

Boston University Biology Professor Gloria Callard told the Post, "What we're witnessing is a snapshot of evolution at work."

Copyright 2006 by United Press International