In May, a sudden burst of rain in Atlanta snarled parts of the city. It also overwhelmed a wastewater tunnel on the Chattahoochee River, dumping untreated sewage into the waterway and killing thousands of fish.
The river is still recovering.
As the climate warms, there’s good reason to believe that such extreme rain events are becoming more common.
Chattahoochee Riverkeeper Jason Ulseth was on the river the morning after the storm. The first thing he noticed was the smell.
“The river just stunk,” he recalls. “It was a darker color, I could immediately tell something was off. And then as I started boating upstream, I started seeing all these dead fish.”
Two weeks later, he was back out on the river to see how it’s recovering.
The closer he got to the beach where he landed his boat, the more dead fish he saw.
Near here, where Peachtree Creek hits the Chattahoochee, a wastewater storage tunnel dumps into the river. Before that, it runs 8 miles under Atlanta.
“We’re right near the discharge,” Ulseth said. “The banks were coated in this black material all up and down, but all of those heavy rains that we got following this overflow seems to have kind of washed it all out.”
Jason dug into the sandy shoreline with a shovel, and pulls out a black chunk the size of a pine cone.
“Smells like sewer sludge,” he said.
That’s what it is.
After the rain event in Atlanta, cars got stranded, rush hour traffic came to a halt, some of the city ended up under a boil water notice, and the city’s wastewater treatment system was completely overwhelmed.
That’s when the rain ejected this sludge from the tunnel. Rotting takes oxygen, and as this sludge rotted, it robbed the river and the fish in it of oxygen. The fish suffocated.
According to the Riverkeepers, the river was running so low that when the tunnel emptied into Peachtree Creek, it was strong enough to reverse the direction of the creek, sending black sewage upstream.
But Ulseth said the river already looks significantly better.
“There’s no more real dead fish to see,” he said. “They’re all decomposed and water levels have dropped back down. The turbidity and water clarity is clearing back up. We’ve seen dissolved oxygen levels coming back up, so all good things.”
Marshall Shephard is the director of the atmospheric sciences program at the University of Georgia. He said this was more than a normal summer storm.
“Candidly, an inch of rain in one hour, that would get my attention,” Shepard said. “So 2 to 3 inches of rain an hour is certainly an extreme event.”
Extreme, yes, but increasingly not rare.
“I think it has the fingerprints of, DNA of what we have long expected as our climate warms,” he said. “Basic physics tells us that as the atmosphere warms, it has more water vapor available to it. And so all of our studies in the peer-reviewed literature are showing us that the most extreme rain events have increased over the last 50 years in intensity.”
And, Shepherd said, Atlanta isn’t designed for this.
“When engineers 30, 40, 590 years ago were designing stormwater management systems, they assumed the rainstorms of 1965 would be like the rainstorm [of] 2026,” he said. “And we know that’s not the case.”
Back on the river, Jason Ulseth said the effects of that storm were shocking.
“It was incredible to see 20-, 30-pound striped bass, catfish that have been thriving in the rivers for years didn’t survive this event.”
So while the river might be bouncing back, it’ll take years for the fish that survived to grow to that size.
Now, the city of Atlanta says it is looking at the tunnel, to better understand just how it was overwhelmed by the rain event in May.
