How we know it's (usually) safe to swim in the Ohio River (2024)

The annual Great Ohio River Swim is scheduled for this Sunday, with up to 250 people expected to swim from the Cincinnati bank to Kentucky and back again.

"It's super fun," said Event Chair Caroline Keating. "We have folks from all levels that come. I did the swim years ago when my grandpa was in his 80s, so you get everybody."

The Summer Olympic Games this year in Paris have a lot of people asking: Is it really safe to swim in rivers like the Seine in Paris and the Ohio in Cincinnati? Both cities have a combined sewer system, which is designed to send untreated sewage and stormwater into the river during heavy rain.

"We're not the Seine," says Brewster Roads, chair of the Ohio River Way Board. "[The Ohio River] is cleaner now than it's been for years, which is just wonderful. You can go swimming in the river these days, not a problem."

But how do we actually know that?

Tracking water quality

The Ohio River Valley Sanitation Commission, or ORSANCO, conducts weekly water quality tests along the Ohio River in Pittsburgh; Wheeling and Huntington, Va.; Cincinnati, Louisville, and Evansville, Ind. This is done from April to October, when people are most likely to consider spending time in the water.

The tests look for the level of E.coli, a type of fecal coliform bacteria that can cause diarrhea; in rare cases, a person infected could experience stomach cramps, vomiting, and fever. E.coli is nearly always present in public waterways like the Ohio River, usually because of animal feces. In areas with a combined sewer system, like Cincinnati, E.coli levels tend to spike right after a heavy rain because of combined sewer overflows into the river.

LEARN MORE: Backed Up, a podcast about the Cincinnati sewer system

The EPA says water is safe for full-contact recreation (i.e., wading and swimming) as long as E.coli levels are below 240 CFU/100mL (that's colony-forming unit per 100 milliliters).

Senior Lead Environmental Scientist Stacey Cochran collects the samples in Cincinnati in six separate locations, including the area where the Great Ohio River Swim will take place. Samples collected on Tuesday, Aug. 20, came in well below the threshold:

• At mile 462.6 on the Ohio bank: 3 CFU/100mL
• At mile 470 (Newport Levee): 33 CFU/100 mL
• At mile 470 (Serpentine Wall): 15 CFU/100mL
• At mile 477.5 (center of river via Anderson Ferry): 67 CFU/100mL

Cincinnati data is collected every week on Tuesdays and published on Fridays along with data from other communities along the river. Cochran says this week, she'll conduct extra tests on Thursday because of the swim event on Sunday.

"If it happens to rain, say, Friday or Saturday, I would go out and do extra testing just to make sure," Cochran said.

E.coli isn't the only pollution concern. Dozens of testing programs look at pollutants like PFAS, nutrient runoff, and harmful algae blooms. The metric the EPA tracks for contact recreation — like swimming or wading — is E.coli levels.

Other kinds of contact — like eating fish caught in the river or ingesting the water directly — is regulated with different metrics. For example, the Ohio Department of Health has a consumption advisory for fish caught in the Ohio River; they could contain PCBs (polychlorinated biphenyls) and mercury. Even then, the advisory is to limit how often you eat fish caught in the Ohio River, not necessarily to avoid eating them altogether.

RELATED: This mobile aquarium teaches people about the Ohio River's biodiversity

"Folks should not be directly ingesting the river water, or creeks or lakes or anything like that," said Richard Harrison, ORSANCO executive director and chief engineer.

Completely separate from ORSANCO, Greater Cincinnnati Water Works conducts extensive testing of the Ohio River as it treats water to send to our taps.

Safely swimming in the Ohio River

When it comes to more than 200 people swimming across the river, Keating says water quality is just one safety measure they look at.

"Last year we had a ton of rain, but the water quality was actually perfect, but the current was really strong," Keating said. "So we had to make a new course so that nobody was swimming all the way across the river for safety reasons. But we take that very, very seriously. We don't want to put anybody in danger ... so we'll make that hard call if we have to."

The Great Ohio River Swim dates back to 2007; in 2017 it was named in memory Caroline's father Bill Keating, Jr. The event raises money for Adventure Crew, a nonprofit that offers outdoor recreation opportunities to teens in 27 high schools in Cincinnati and Northern Kentucky.

"We're teaching our urban teens how to swim," Keating said. "I'm happy to say that last year, we had a teen that went through the swim program and then went on to become a city lifeguard."

Cincinnati struggled over the past few years to hire enough lifeguard to open all public pools; 2024 is the first year since 2019 that all 24 pools are open.

Listen to Backed Up

Learn everything you need to know about combined sewer systems in Backed Up, a new podcast from Cincinnati Public Radio. Available at wvxu.org/backedup or wherever you get your podcasts.