But if you're on the river, there's no way of knowing that. That's because the National Park Service isn't posting signs to warn anglers and kayakers when levels of E. coli have climbed dangerously high.
It's not like the Park Service doesn't have the signs. They're already made, but they're in storage somewhere. And that's just where the Chattahoochee Outdoor Center, the company that rents canoes and rafts for trips down the river, wants them to stay.
If the park service installed those warning signs, says the center's operator, Ken Gibbons, his business "would absolutely be hurt. Everybody needs to be concerned about it, I know, but the testing has already been done."
Actually, water samples are taken four times a week from Medlock Bridge and Paces Ferry and tested at the USGS lab in Norcross. There, USGS employees treat the water, and let the E. coli cultures incubate.
The National Park Service recommends avoiding water that has more than 236 E. coli colonies per milliliter, which can put you at risk for diarrhea, fever, nausea, ear and nose infections, and worse. But E. coli levels along the stretch of the Chattahoochee tested by the USGS routinely soar above those levels.
Take May 29. On that day, thunderstorms pummeled the metro area, and the sewage treatment plants flooded with stormwater and spilled untreated sewage into the Chattahoochee and its tributaries. After the May 29 rain, E. coli levels shot up to 5,326 colonies per milliliter -- 22 times the recommended limit.
These findings aren't any secret; they're posted on a USGS website -- which gets a measly 100 hits a day.
Last December, David Ek, who heads the park service's portion of the project, ordered several signs that would show park visitors the same thing Web surfers could see -- whether there was a low, medium or high risk of getting sick. He planned to put up the signs along 48 miles of the river, including areas around the Chattahoochee Outdoor Center's rental stores.
Ek recalled his first conversation about the signs with the center's operators: "You can imagine that they had some issues and concerns. If I had their business I'd be concerned about [the warning signs] too."
Says Ek: "We of course want to make sure we don't go blindly into anything whenever we are dealing with a public health issue that has a bearing on ... the economic value of their business."
In other words, public health -- at least for now -- is taking a back seat to business concerns. Ek says he's waiting for the signs to clear some bureaucratic hurdles before they're installed.
Gibbons, however, says test results aren't a true indication of the Chattahoochee's water quality. "The tests take a minimum of 24 hours, so by the time people see the results posted, that water they tested is 24 hours downstream," he says.
Granted, that's not a bad point. But because of Atlanta's antiquated sewage treatment plants, E. coli counts in the river regularly -- almost weekly -- exceed the high-risk threshold, especially at the Paces Ferry sampling site, which is downstream from five wastewater treatment outpours and not too far from the popular kayaking spot, Devil's Race Course.
Matt Kales, the River Basin Protection Manager for the Upper Chattahoochee River Keeper, fly fishes the Hooch at least once a week. He releases his fish because state environmental officials warn against eating fish caught in the Hooch. Mercury, it seems, isn't something humans should ingest.
Kales thinks the E. coli in the water caused what he calls the "creeping crud" infection he has in his eyes. He probably wiped too close to his eyes too soon after he handled his fishing line, he says.
Kales is one of the River Keeper's volunteers who couriers water samples to the USGS four mornings a week. "I say this with all due respect for the economic interests the concessionaires have in this river: is it responsible to put people in the river and expose them to such high levels of bacteria?"
That's an easy one -- the answer is no.
For more on E. coli levels in the Chattahoochee River, log on to http://ga.water.usgs.gov/bacteria