Is it safe to swim in the Delaware or Schuylkill? What about Devil’s Pool? It’s complicated.

On a recent day, seven teens from Philadelphia’s scrappy Kensington neighborhood took turns clambering onto a tree limb or grasping a rope swing, and then plunging with a whoop into the Delaware River 15 feet below.

“This is like a neighborhood beach,” said Chris Hall, 14, as he climbed up wooden slats braced against a concrete wall, grabbed a railroad spike sticking out of the top, and gave a heave to emerge from the water. He doesn’t think it’s dirty at all.

“It don’t bother none of us. If I saw a dead body or something like that, I’d be worried,” Hall said with a grin.

The federal Clean Water Act of 1972 regulated pollutants in U.S. waterways with the laudable goal of making then-filthy major city rivers "fishable and swimmable” by 1985. Certainly, not all waterways are swimmable even in 2019, but they are much cleaner. Some portions of the Delaware are swimmable based on bacteria levels.

Other portions are not, including where the teens gathered near the defunct Pier 18, also known as Graffiti Pier. Their beach is a spit of dirt amid a concrete harbor that housed rail-yard operations in Kensington’s industrial heyday.

Pollution is far from the only issue. There are good reasons that you rarely see anyone swimming in the urban Delaware. Drowning and being struck by boats and drifting debris are real risks. The city has an ordinance against swimming in areas not designated as safe based on suitable access, currents, river traffic, and other factors. The river is tidal from the Delaware Bay up through Trenton, so currents can be swift and strong.

States decide what waterways are swimmable. So Pennsylvania, New Jersey, Delaware, and New York all set their own standards based on counts of E. coli, a fecal coliform bacterium found in the intestines of animals and humans, and enterococci, an indicator of fecal bacteria. Levels can spike when the city’s sewage treatment system is overwhelmed during heavy rains, sending untreated wastewater into the river and its tributaries.

Portions of all four states lie within the Delaware River Watershed, meaning they all send water into the river. In Philadelphia, the Schuylkill and the Pennypack, Tacony, Darby, Cobbs, Poquessing, and Wissahickon Creeks all flow into the Delaware.

Under government rules, swimmable means that if you take in a little water by accident while swimming or boating, it isn’t likely to make you sick. Stretches of water or whole waterways deemed suitable for swimming and boating are known as “primary contact waters.” Those labeled “secondary contact waters” mean it’s OK to boat or fish, but swimming isn’t a good idea. (Definitions of swimmable do not include chemicals or other substances in the water.) A single waterway can have stretches that are swimmable and others that are not, depending on where and when testing was carried out.

Bacterial indicators are down from their 20th-century peaks because the Clean Water Act forced municipal sewage treatment plants to clean up their acts, and regulated the chemicals and waste products industry can release into the water.

However, the Delaware is far from pristine. The Philadelphia Water Department has its Green City, Clean Waters program to help reduce sewage overflow after heavy rains, but the old sewage system can’t prevent contaminants from reaching the river. Other pollutants also make their way into the water during storms, including trash, fertilizers, and chemicals that run off roadways, farmland, and other property.

Another threat could be politics. Environmentalists fear a number of actions by the anti-regulation Trump administration could weaken water protections. They cite the failure so far of the Environmental Protection Agency to set federal limits on PFAS contaminants in drinking water, though the agency is moving toward setting maximum levels. And, they cite, among other issues, recent changes to the Endangered Species Act that could remove protection for some waterside habitat.

After one of the warmest springs on record, toxic blue-green algae has closed some of New Jersey’s largest freshwater lakes this summer, including Hopatcong and Musconetcong, both within the Delaware River Watershed. Though the cyanobacteria exist naturally, pollutants from septic systems and lawn fertilizers can fuel their growth, as can heat.

But, for now, all of the main stem of the 330-mile Delaware River — except as it flows through Philadelphia — is swimmable from the perspective of the Clean Water Act.

The Delaware River Basin Commission, an interstate federal regulatory agency that oversees water quality in the watershed, puts a no-swim zone from about Bleigh Avenue, a few miles north of where the Kensington teens were swimming, all the way south to the Delaware state border. Every two years, the agency compiles a water-quality report for the EPA.

New Jersey, which uses more stringent bacterial guidelines, puts the no-swim zone from the Delaware state line all the way up to Trenton.

The River Network, a national nonprofit, issued a new interactive map this month that people can use to figure out what’s swimmable. The Pennsylvania Department of Environmental Protection also has its own interactive map, which indicates which waterways meet recreational designations.

Another nonprofit, Delaware Riverkeeper Network, has launched a survey to see who swims in the Delaware.

John Kenny, of Conshohocken, swims in the Schuylkill several times a week, but stays miles above the Philadelphia limits. Kenny owns French Creek Racing and trains triathletes in the river near Valley Forge. He met on a recent day with Christina Cunningham, Barbra Bateman, Diane McManus, and Laurie Hug. The group trains together for races.

“We train in there at least three times a week,” Kenny said. “It’s somewhat contingent on the water. Any major river in a populated area is going to have the same issues. There’s all kinds of runoff and it causes a lot of turbidity, and the fertilizers from lawns, geese waste, and anything on the roads upstream will make its way into the river during big rains. Anything like that will cause an increase in bacteria counts.”

In recent years, he said, the number of major rainfalls has increased, and with them, more treacherous waters.

Kenny uses the Philadelphia Water Department’s Rivercast website, which updates water-quality levels hourly for the Schuylkill between Manayunk and Boathouse Row as an indicator of whether he should swim, though he’s farther upstream. He uses water-flow data from U.S. Geological Survey gauges to determine if the water is running too fast. He also coordinates with the Valley Forge Watershed Association for information. And, he ensures swimmers can handle the current.

The portion of the Schuylkill in Philadelphia, from below Fairmount Dam to around Bartram’s Garden, is tidal and not suited to swimming. The Schuylkill above the dam in Philadelphia is designated for swimming; but Philadelphia regulations require a permit, usually reserved by triathlons. Rivercast provides a reading of green, yellow, or red, as to whether segments of the Schuylkill in Philly are clean enough for recreation.

Gayle Killam, director of the River Network’s Clean Water Act Program, said that though the creek appears clean to the eye, it is listed as an impaired waterway because of pollution.

Cresheim Creek, a tributary of the Wissahickon, feeds rock-lined Devil’s Pool, a popular swimming spot in Wissahickon Valley Park. Though Cresheim has not been assessed for recreational uses, the Wissahickon is listed as impaired. In addition, the city prohibits swimming at Devil’s Pool, though that doesn’t seem to stop swimmers from plunging in on swing ropes.

“If you look at Devil’s Pool, it is beautiful," Killam said. “But it’s not just potentially dangerous from people hitting rocks. The water is also impaired."

Generally waterways in Camden County, such as the Cooper River and Pennsauken Creek, are not swimmable, based on the River Network map.

In Burlington County, portions of Rancocas Creek along the Delaware are swimmable but become impaired farther inland. It’s not really until the Pinelands that the waterways clear up enough for swimming.

In Gloucester County, just a part of Raccoon Creek is swimmable near the river. It’s not until Salem County that the waterways become much cleaner.

It’s advisable to check the River Network before taking any plunges around the watershed. But that doesn’t seem likely for the Kensington kids enjoying their concrete beach.

Jonathan Rodriguez, 14, said he had no worries about the water.

Then he leaped off a tree limb into the Delaware.

Editor’s Note: “From the Source: Stories of the Delaware River” is produced with support from the National Geographic Society, the Lenfest Institute for Journalism, and the William Penn Foundation. Editorial content is created independently of the project’s donors.

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