Christopher Swain, 36, has spent the past month swimming down the 60-mile-long Charles River -- from northeast Massachusetts to Boston Bay -- to focus attention on the plight of the river.
"I have a crazy dream," he said. "I want the Charles River to be swimmable. People think of it as a reeking beast of a waterway. They think, 'Oh, there's no way I'd go in there. I'd have to burn my clothes. I'd have to go straight to the hospital.' And I am here to say it doesn't have to be like that."
The story of the Charles River is much the same for many of the country's favorite rivers -- pesticides and other chemicals are destroying its ecosystem.
The frigid northeast temperatures haven't put a damper on Swain's spirit.
"Chilly today, 47 degrees I think," he said. "For 45 minutes I'll have a massive ice cream headache and then hopefully it will go away. Crazy."
While other people bike, ride and run for causes they care about, Swain has already swum down the Hudson River (315 miles), across Lake Champlain (129 miles) and through all 1,200 miles of the Columbia River, which rises in British Columbia and spills into the Pacific Ocean on the coast of Washington.
Because of the polluted waterways, Swain is risking his health to further his cause.
"The most contaminated piece of land for instance in the entire Western Hemisphere is the Hanford Nuclear Reservation in southeastern Washington," Swain said. "The Columbia River flows right through it, and I swam right through there, not because I'm totally insane, but because I wanted to say, 'We should do something here.' I had seven ear infections, four bad respiratory infections. Three different times I had infections in my lymph system, lymph nodes that swelled up to golf ball size."
To prevent parasites and bacteria from making him sick, he takes a break every 600 strokes -- he actually keeps count -- to gargle with hydrogen peroxide.
"I think I have swum into every old car, refrigerator, washer, dryer and tire that's ever been thrown into the river," he said.
Swain says that he learned from his father the importance of doing something he loved and something that mattered.
"I think what happens when I get up in the morning and I look down the barrel of another day in cold, dirty water -- when I'd rather be home, when I'd rather be playing with my kids, when I'd rather, heck, be warm at any desk job -- I realized that if somebody doesn't put themselves on the line, nothing changes."
Swain has always loved the water.
"I don't know when it started but I remember having trouble getting out of the ocean when I was 5, 6, 7 years old. And my mom trying to crack the whip, 'Come on. It's time to go.' "
All the swimming keeps Swain, an acupuncture specialist, away from home a lot. He misses his wife and two small daughters. His oldest daughter's first sentence was "Daddy swims in the river."
The Charles River is much cleaner than it was 10 years ago, but sewage and garbage are still a big issue. Swain often takes a break from swimming to clean up trash with community groups and schools.
Over the winter, he'll talk to thousands of schoolchildren about the rivers and work with teachers to create curriculum for future learning. He has offered his services to any city with a river that needs similar attention.
"It's not just about the Charles River or the Hudson or the Columbia River," he said. "This is about all the waterways in the world. We're going to have to see the connections between what we do and what happens with the water and the Earth and the places that we live. If we can make that leap, we're going to be happier people, and we're going to be living in a better world. I, for one, hope we get there."
Peter Jennings filed this report at World News Tonight.
For more information visit www.swimforcleanwater.org