On a warm July morning about 15 years ago, Ellen Weinberg climbed a metal fence in lower Manhattan wearing a bathing suit, goggles, and swim cap, walked up to the banks of the East River, and plunged in. About 30 minutes later, passersby on the Brooklyn side of the river, near what is now part of Brooklyn Bridge Park, gaped as Weinberg and four other swimmers emerged from the water.

“Everybody was looking at us like we were crazy,” says Weinberg, now 58. “It was so fun—I really felt like Kramer,” she says, referencing the Seinfeld episode where the kooky character, tired of overcrowded pools, goes for lengthy swims in the East River.

It may sound like a caper, but Weinberg’s dip was a permitted event: She and the other open-water swimmers were testing how difficult it was to cross the river, with its swift currents and changing tides. (A motorboat accompanied them for safety.) Weinberg has been in the river a few times since, and yes, she’s quite healthy.

For many New Yorkers, the idea of swimming in the East River is as palatable as guzzling hot dog water or snuggling with a Port Authority toilet seat. But opening the city’s rivers to public swimming is a dream that unites city planners, environmentalists, and water lovers. It could be crucial to the city’s post-Hurricane Sandy climate change resiliency—and it might not be as much of a pipe dream as you’d think.

One developer is already thinking about it: Last month, Two Trees announced plans for a massive project in Williamsburg that would include two 650-foot mixed-use towers on River Street and a six-acre park on the East River. The park would soften the area’s relationship with the water: Instead of the hard promenade seen at nearby Domino Park, or the craggy boulders of East River State Park farther north, the new site would let people walk right up to the water and interact with it at a wading beach, kayak launch, and educational pier. It would help break wave action and absorb floods from storms and rising sea levels, while protecting Two Trees’ own property.

And eventually, the developer wants to create a swimming spot that would be open to the public and enclosed from the river’s turbulent wake, which would put New Yorkers in direct contact with the East River for the first time in generations. It would not be filtered, like the proposed +Pool—just pure, natural East River. Lisa Switkin, a senior principal with James Corner Field Operations and the park’s lead designer, predicts that it could happen within a decade; if successful, other developers could follow suit.

“We’re a city that has decided not to retreat,” Switkin says. “And if you’re not going to retreat, you have to change your relationship with the water. This whole idea of living with water instead of fighting it is something that has become a new way of thinking in resiliency.”

The model for this is the Copenhagen harbor baths, a public swimming area in the once-polluted Copenhagen Harbor that has transformed into a popular, beach-like destination. That body of water also once seemed hopeless: In the 1960s, residents would see dead fish wash up on its shores; in the 1990s, wastewater was still pumped into the site where people now line up for an after-dinner dip. In the early ’90s, the city began an aggressive program to improve water quality and reclaim its aquatic environment, and by 2002, the first harbor bath was open. (Last year, CNN named Copenhagen the best city in the world for swimming.) The same company that built that first bath—Bjarke Ingels Group—is working with Two Trees on the Williamsburg project.

“Initially the community was a bit hesitant, probably similarly to this location, to engage with the water,” Tony Shiber, an architect with BIG, says of the Copenhagen project. “While this is a much more dense environment, the challenges are also similar in terms of changing the way people perceive the water.”

And here’s the thing: You could swim in the East River now, in theory. A report from the NYC Department of Environmental Protection released in October says the city’s rivers, harbors, and bays are cleaner than they’ve been since the Civil War. Yes, you see plastic bags and brown muck pooling around the rocks at the riverside, but the middle of the river—a great force of nature formed by a melting glacier 11,000 years ago, whooshing water from Long Island Sound through the city out to Upper New York Bay—is deep, clean, and ever-moving. The city spent $45 billion over the last four decades to improve water quality, including upgrading sewage treatment facilities and adding green infrastructure to reduce runoff, all while industry that once polluted the waterfront died off.

But two big problems stand in the way of public river swimming. The first is rain: Rainwater picks up everything on the street—from motor oil to dog poop to cigarette butts—and sends it to the same pipes as sewage, a phenomenon known as combined sewer overflows (CSOs) that’s tracked through a delightfully niche Twitter account. The muck overloads the wastewater system, and it ends up getting flushed out into the waterways. For about 48 hours after a heavy rainfall, the waters are brimming with bacteria like the streets of the Lower East Side after last call on Saturday night, and swimming is, unsurprisingly, ill advised.

About five billion gallons of this mix of sewage and garbage flows into the East River each year, out of about 20 billion gallons for the whole city (the Hudson gets only about 725 million gallons a year). And that’s still a huge improvement from the 110 billion gallons that were dumped citywide in 1985.

“The city really has to make the waterways swimmable every day when people want to swim, not just days when it’s sunny,” says Shino Tanikawa, executive director of the NYC Soil & Water Conservation District. “That’s going to be really difficult thing to do.”

Fixing the sewer system is something environmental advocates says is integral to the city’s long-term resiliency efforts. New York was built out of concrete and pavement, not material that sucks up that water. A city built for the future, advocates say, would be more porous and green: using permeable pavers instead of asphalt parking lots (or, better yet, no parking lots at all); green roofs replacing the need for gutters; and more micro green spaces on the street, all of which would suck up more of that rainwater.

The other issue is the river’s image. The East River is often seen as less romantic and dirtier than its mightier sibling, the Hudson, whose name evokes the pristine springs of the Adirondacks where it originates. The Hudson is the city’s moat, separating New York from the rest of the country, as documented in Saul Steinberg’s famous New Yorker cover. But the East River, pushing through four of the five boroughs like a harried commuter, is an inside joke. In that Seinfeld episode, Kramer is mistaken for a dead body; the stench of the river follows him all day.

“The public who is not involved in this issue closely still think the East River and Hudson River are so polluted that if you fall in you’re going to need a tetanus shot or grow a third arm or third eye,” says Tanikawa.

Skeptics often ask Capri Djatiasmoro, the race director for Coney Island Brighton Beach Open Water Swimmers, who has participated in an annual marathon swim around the island of Manhattan, if she gets inoculation shots before entering the East River. “Oh yes, we do shots,” she says. “After a swim we do shots of tequila or Bacardi. That will kill any bug you pick up.”

Cutting down on the raw sewage going into the river would certainly help its image. The city has 139 combined sewer overflow points along the East River and the western portion of Long Island Sound. In 2018, the East River had at least 82 days of overflow, says Mike Dulong, senior attorney for Riverkeeper, a group that advocates for clean waterways; there were 179 days of overflow citywide.

The city and state this month will debate a long-term plan to upgrade stormwater management. But environmentalists say it isn’t robust enough, especially if swimming is on the horizon. It calls for things like rain gardens (more than 4,000 have already been installed throughout the city), or retrofitting public property such as playgrounds with pervious materials that can absorb water. But much of the property in the city is private, and critics say the plan needs to better incentivize landowners to incorporate green infrastructure in their projects.

“There are very few incentives for developers to put on a green roof and do green practices,” Dulong says. “If developers would do that it would have enormous benefits for CSOs and water quality.”

The public still thinks the East River is so polluted that if you fall in you’re going to need a tetanus shot.

Dulong is hopeful for river swimming one day; he lives in Williamsburg and often runs right past the proposed Two Trees site. But he questions whether building any structure in the East River—even a swimming enclosure—is a good idea. “The East River has been battered,” he says. “We’ve basically killed everything that’s in the channel area.”

And trading a giant development for a place to meet the water may not be worth it, Tanikawa says, especially for the people living in the proposed residential towers, who may end up navigating a flooded building if another Hurricane Sandy blows through.

“Why couldn’t we envision this kind of waterfront, not as an amenity in exchange for building, but for its own sake?” she asks. “This is the kind of waterfront we should have a lot more of, whether or not it’s residential.”

Two Trees representatives say the River Street plan addresses both of those concerns: It would help bring more life back to the waterfront by creating marshes, oyster beds, and feeding and nesting places for species such as Atlantic blue crab, blue fish, and mussels. And from a resiliency standpoint, the design of the public park would help stem flooding in the towers because its expanded soft shoreline and pier will break wave action and absorb flood waters, while the towers will keep sensitive electrical and mechanical equipment above the floodplain.

The plan also could also help unlock new uses for the city’s waterfront, which advocates and city officials have called the “sixth borough” because of its untapped potential. Even politicians gotten in on it: In 2011, then-Mayor Michael Bloomberg launched a plan for new waterfront parks and a ferry service, saying, “Our waterfront and waterways—what we are calling New York City’s ‘Sixth Borough’—are invaluable assets. And when our work is complete, New York City will again be known as one of the world’s premier waterfront cities.”

Increasing use of the river is one way to fast-track clean-up; it would be an induced demand, similar to how increased bike lanes are linked to overall pedestrian safety. All it would take is one public swimming spot for New Yorkers to reimagine the river from a waste-flusher to a pristine amenity: Imagine being stuck on the bridge in a hot, crowded subway car, looking down at the river below and fantasizing about jumping into its cooling waters as soon as you get home.

Weinberg remembers getting that unique perspective in for the first time on that test swim, and realizing she liked the East River better than the Hudson.

“When you’re swimming in the East River, the views … are gorgeous, just gorgeous,” Weinberg says. “I’m an urban swimmer. I like seeing buildings.”

Correction: An earlier version of this piece misstated the number of overflow days citywide; the number is 179 days citywide, and 82 days for the East River alone. Curbed regrets the error.