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.
Here's a sampling of where other efforts to reclaim urban rivers for swimming stand:
The city partnered with a local civic group to entice residents to take a dip in the Willamette River this summer.
They opened the first official public beach with lifeguards on the river earlier this month. They've also launched a public awareness campaign and scheduled a range of water-centered events.
Among them was last weekend's Big Float inner tube river parade that drew about 2,500 revelers.
A group of architects, designers and engineers have proposed a series of pools in the middle of the iconic River Thames, where river water would be constantly filtered.
Chris Romer-Lee, a lead organizer of the Thames Baths project, said the group aims to submit plans to local authorities by early 2018.
The group launched an online crowd-funding campaign last year that raised about $182,000 to refine their design but are working to secure almost $19.6 million in outside investment for the project itself.
Four local artists and architects launched the idea for +Pool , a floating, filtered pool in the shape of a plus sign in 2010.
Since then, they've successfully tested a filtration system that removes bacteria without using chemicals, said Kara Meyer, deputy director for the nonprofit effort.
She said organizers also have raised nearly $2 million to continue developing the project, are exploring potential sites on the East and Hudson rivers and are preparing to seek necessary city approvals.
The nonprofit Yarra Swim Co. unveiled its concept for a floating pool on the city's Yarra River at Australia's Venice Biennale Exhibition last year.
Michael O'Neill, the effort's co-founder, said the company will be reaching out to community groups and government agencies starting next month to get their feedback on what the Yarra Pools project should offer and to promote its broader vision for use of the river.
The long-gestating Flussbad project calls for cleaning up a canal off the German capital's Spree River for public bathing.
Barbara Schindler, a spokeswoman for the effort, said the idea has been around since the 1990s, but has reached notable milestones in recent years.
She said the organization completed a water quality study in 2015 and has received $4.6 million in government funding to hopefully turn the concept into reality.