The eastern United States is dotted with dams, blocking streams and rivers of any size. The explosion of industry in the U.S. led to damming of any possible source of power for mills.
As those dams are removed, scientists are beginning to observe toxins of all types from the dams. The list is like a trip back through the pollutants of the last few hundred years: from lead to pesticides to iron to charcoal, each industry has left its mark.
Scientists aren't sure the best way to limit the spread of these toxins, which until now were trapped in the sediment near the dams. As the dams are removed, the toxins are set free into the waterways.
See the story at Discovery News.