They dove in, splashed around and blissfully floated in the murky river water.
Intrepid swimmers got a once-a-year chance to beat the summer heat with a dip in the once-notorious dirty water of Boston's Charles River on Tuesday.
The annual "City Splash" is one of the few days the state permits public swimming on the city's stretch of the 80-mile river, which gained notoriety in the Standells' 1960s hit "Dirty Water."
The event, now in its fifth year, spotlights the nonprofit Charles River Conservancy's efforts to build a permanent feature on the river that would allow visitors to enjoy the water without coming in contact with any leftover contaminants. They call it a "swim park," which would include floating docks for swimmers to safely jump into the river without touching the hazardous bottom. The water quality would be regularly tested.
Nearly 300 people signed up to take the plunge.
"It felt refreshing and wonderful," said Ira Hart, a Newton, Massachusetts, resident as he hopped out of the river, goggles in hand. "They used to talk about how it was toxic sludge and you'd glow if you came out of the Charles. Well I'm not glowing, at least not yet."
Boston is among the cities hoping to follow the model of Copenhagen, Denmark, which opened the first of its floating harbor baths in the early 2000s. Paris opened public swimming areas in a once-polluted canal this week, and similar efforts are in the planning stages in New York, London, Berlin, Melbourne and elsewhere.
In Boston, the Charles River Conservancy still needs to raise a few million dollars and garner approvals from state, federal and city agencies.
But S.J. Port, the group's spokeswoman, said the biggest hurdle already has been overcome: The Charles is now among the cleanest urban rivers in the country.
The U.S. Environmental Protection Agency announced this month the river earned a "B" grade for water quality last year, meaning it met the standards for boating 86 percent of the time and 55 percent of the time for swimming. That's a marked improvement from the "D" the Charles was given in 1995, when cleanup started in earnest, but down from 2015's "B+" grade.