Are Providence's rivers as clean as the Seine? They're comparable, but don't plan on swimming.

PROVIDENCE – Much has been made about water quality improvements in the Seine that are making it possible to hold some Olympic swimming events in the river that runs through the heart of Paris.

Thanks to a new $1.5-billion system to take care of sewage overflows into the river, bacteria counts dropped enough to allow the swimming portions of the men’s and women’s triathlons to take place earlier this week, with the mixed relay triathlon and a couple of long-distance swim races set to be held in the river next week.

The improvements in the Seine got us thinking about Providence’s own urban rivers and the strides in water quality that have come with similar efforts to control overflows from the combined sewer system that serves Rhode Island’s capital and its environs.

Have they been successful enough to allow swimming in the stretches of the Woonasquatucket and Providence rivers that flow through downtown Providence?

The short answer is no, at least according to the state’s water quality regulations.

But that doesn’t necessarily mean the rivers are dirtier than the Seine.

Here's what monitors test for to know if a river is clean enough for swimming

Olympics organizers held their collective breath after a downpour during the opening ceremony on Friday caused bacteria levels to spike in the Seine.

It was a comedown after the mayor of Paris took a highly publicized dip in the river leading up to the games to signal that its waters were safe enough for some of the world’s best athletes.

But the change in fortunes demonstrated how dependent the water quality in the river is on the weather. Just as in other older cities with antiquated sewer systems, no matter how much is invested in infrastructure, a heavy downpour can make all the difference.

Environmental authorities determine whether bodies of water are safe enough for swimming based on how contaminated they are by human or animal waste.

To make their determination, they generally test for certain bacteria that are present in the intestines of warm-blooded animals. They include fecal coliforms, of which E. coli is one type, and Enterococci.

While these bacteria usually are harmless to humans, they’re seen as indicators of the presence of more dangerous organisms, such as bacteria that cause cholera, dysentery or typhoid.

What are the standards to know if the Seine is clean enough for swimming?

Not all jurisdictions test for the exact same bacteria. Standards also vary from one place to another.

To gauge the safety of the Seine’s waters, the Olympics adopted the water quality standard set by the World Triathlon Association.

For inland waterways like the Seine, levels of E. coli cannot exceed 900 colony-forming units per 100 milliliters, while levels of Enterococci cannot be greater than 330 units per 100 milliliters, according to the governing body’s rules.

In the months before the games, bacteria levels fluctuated wildly, with E. coli counts at times surging to 10 times the limit and Enterococci to six times the standard.

One seven-day period leading up to the opening was typical of the roller-coaster ride in contamination concentrations, with numbers well below the standards at all the testing stations until a rainstorm sent levels of both types of bacteria at the Alexandre III bridge, the starting point of the triathlons, to more than double the limits.

It took another two days for the water to clear then. And something similar happened after the rain over the weekend.

By Tuesday morning, testers said that E. coli results had come in between 488 and 770 units. It’s unclear what the levels of Enterococci looked like.

Organizers determined that the Seine had cleared enough to allow the triathletes to immerse themselves in its waters and, after a one-day delay, the races went ahead on Wednesday.

Rivers in Providence compare favorably

So how do the downtown rivers in Providence compare with the Seine? Not too badly, it turns out.

Because swimming isn’t allowed in the rivers, or is even being considered, testing is infrequent and not done widely.

It’s also not carried out by the state. The Department of Environmental Management focuses on testing waters used for shellfishing. The Department of Health concentrates its testing efforts on beaches already licensed for swimming.

But the Woonasquatucket River Watershed Association does do monthly bacteria tests at several stations on the Woonasquatucket during the warm-weather months as part of the University of Rhode Island’s Watershed Watch program.

Last year at Waterplace Park, Enterococci levels ranged between 148 and 1,201 units, with a geometric mean of 364, which is pretty close to the standard being used in Paris. This year, so far, levels have been higher – between 109 and 4,106 units, with a geomean of 888 – because of all the rain in the spring and early summer.

Just like in Paris, the weather makes a big difference in water quality in the Woonasquatucket, which combines with the Moshassuck River just east of the basin in Waterplace Park to form the Providence River.

Even though the ongoing construction of a combined sewer overflow system that includes a 3-mile-long tunnel under Providence has made a huge difference in water quality in the rivers that flow into Narragansett Bay, the new infrastructure still gets overwhelmed during deluges when large amounts of rain fall in small windows of time – a phenomenon becoming more common with climate change, because a warmer atmosphere can hold more water.

“While the tunnel under Providence has really reduced the combined sewer overflow into the bay, there is still a lot of work to be done to reduce direct runoff (and the contaminants it contains) into our streams and rivers,” Elizabeth Herron, director of Watershed Watch, said in an email.

If you look at Enterococci levels upriver on the Woonasquatucket, but still in a heavily developed part of the city, they’re better than the level downtown. At Donigian Park, the geomean was 259 units last year, and this year it's at 346 so far.

As for E. coli, it’s hard to make an apples-to-apples comparison to the Seine. In Rhode Island, testers sample for all types of fecal coliforms, rather than only E. coli.

But the waters at Waterplace Park did pretty well last year in a rough comparison, with a geomean of 323 units, with a low of 86 and a high of 2,098. At the low end, that’s below this week’s numbers in Paris.

This year, again because of the rain, has been a different story, with a geomean so far of 3,069 units.

But swimming is still not encouraged in downtown waters

Despite the somewhat promising numbers in the Woonasquatucket, swimming isn’t encouraged.

The Rhode Island Department of Health's regulation on water quality for swimming is much stricter than the standard being used in Paris.

The state uses Enterococci levels only to determine swimming safety, and the allowable cap for a one-time sample is 60 colony-forming units per 100 milliliters. For non-designated swimming areas, the geomean of samples must be below 54 units, and for licensed beaches, the standard for a geomean is 35 units.

Why use Enterococci as the standard and not E. coli?

“Enterococcus is preferred because it is more specific to fecal contamination and better correlates with gastrointestinal illnesses,” said health department spokesman Joseph Wendelken. “While E. coli is commonly used as an indicator, it is less effective in saltwater environments where it does not survive well. Enterococcus is more resilient in marine conditions so deemed more reliable.”

Numbers of the bacteria are still high enough from discharges into the Providence River during rains that the waterway is considered impaired by the U.S. Environmental Protection Agency for both swimming and boating.

“Individuals choosing to swim outside of licensed beaches are advised not to do so in waters that are impacted by known pollution sources and not to swim in proximity to storm drains particularly after rainfall,” said DEM spokesman Evan LaCross.

Sewer project has made big difference in water quality around Providence

Still, LaCross said the combined sewer overflow project has been “the single biggest factor” in water quality improvements in the Providence River in recent years. And many independent scientists and environmental groups have said the same.

The $1.7-billion project is still under construction, with work wrapping up on a new section that includes a 2.2-mile-long tunnel under Pawtucket.

The positive impacts of the storage network on water quality have included the announcement in May that Crescent Park Beach in East Providence will be licensed as swimmable and reopened by 2026, a century after it closed to swimming, and the reopening in 2021 of shellfish grounds in the lower Providence River that had been closed since World War II. (Some even say the water is too clean, but that has to do with other changes to wastewater treatment.)

The state uses fecal coliforms counts to determine the safety of shellfish waters, measuring results against the Food and Drug Administration standard of 14 colony-forming units per 100 milliliters. Coliform counts in the newly reopened grounds in the lower Providence River, which are located south of Gaspee Point in Warwick and Bullock Point in East Providence, averaged from 2 to 8 units between 2019 and 2023, according to the DEM.

To get a sense of how bacteria counts have come down elsewhere in the Upper Bay, you can look at data compiled by the Narragansett Bay Commission, the largest wastewater treatment operator in the state and the entity ordered to carry out the combined sewer improvements by the DEM.

The commission tests the water at 20 stations twice a month. Though it doesn’t test in the river waters in the heart of downtown, it does take samples a little downriver, from the Point Street Bridge near the Fox Point Hurricane Barrier.

In 2006, before any of the new infrastructure came online, fecal coliform counts varied from 230 units to 110,000, with a dozen tests in the thousands or tens of thousands. Enterococci numbers maxed out at more than 4,000, with several samples in the hundreds.

Enterocci counts haven’t been more than 85 units this year, and fecal coliform numbers haven’t topped 430.

Of course, the numbers still vary widely and they can still climb pretty high after big rains, but the commission has found that overall bacteria numbers on average are down by half in Narragansett Bay.

This article originally appeared on The Providence Journal: Providence's rivers are as clean as the Seine's, but no swimming allowed