"There used to be an odor, you used to see things floating in the river, but now you're going to see bubbles while the herrings make their migration," Leighton said.

The river's improvement is so dramatic that it looks nothing like it did thirty years ago, river advocates said.

"The only thing you could see at the MIT beach back then was carp,

One of the sturdiest fish," said Roger Frymire, a volunteer for the Charles River Association. "Up in Nashua, there was a paper company literally turning the river a different color every day."

The effort to save the river came from a combination of community action and government support.

"This really began back in the 1970s with the Clean Water Act, but the efforts of the Charles River Watershed Association show what a good nonprofit can do with some good science," said Roger Abele, a local EPA official who has been paddling on the Charles for the past 30 years.

For the past 7 years, the Charles River Watershed Association has taken samples for research into the river's condition. This year, volunteers took over 300 samples from 10 different sites to find sources of contamination in the river. The association then uses this information to inform public officials about problem areas.