Science & Nature
Is the Chicago River St. Paddy’s Dye Job Bad for Fish? One Scientist Says They Don’t Seem to Notice
Dyeing the Chicago River green for St. Patrick's Day is a decades-old tradition. (Tzido / iStock)
The Chicago River is about to get its annual St. Patrick’s Day dye job on Saturday.
This decades-old tradition routinely attracts tens of thousands of revelers to the riverfront, but in recent years it’s also attracted criticism from environmentalists.
Sure, the spectacle of a neon ribbon of green snaking its way through downtown’s skyscrapers looks cool, especially on social media, but what about the harm the dye causes the river’s ecosystem, including the fish that live in the waterway?
At least one scientist says the fish don’t really seem to object to whatever Plumbers Local 130 is adding to the river.
Austin Happel, a researcher at the Shedd Aquarium, tagged nearly 100 fish back in 2023 and has been tracking their movements via “pings” on the close to three dozen acoustic receivers he’s positioned up and down the river.
On St. Paddy’s Day 2024, five of Happel’s tagged fish were hanging out in the Riverwalk section of the river when motorboats began dispersing dye into the water.
Nothing happened.
Per Happel’s observations, there were no changes in behavior that would indicate the fish were in any way aggravated by the dye.
By contrast, a massive rainstorm in July 2023 sent fish scrambling when the city’s sewers were overwhelmed and wastewater was dumped into Bubbly Creek on the river’s South Branch.
The fish fled Bubbly Creek. “They were searching for somewhere to hide, to get out of the bad water,” Happel said.
The moral of this particular story, he said, is that while the high-profile dyeing of the river has drawn a good deal of scrutiny, incidents like combined sewer overflows have a far greater impact on fish, but typically occur out of sight.
“We’ve yet to see a fish kill” during the river dyeing, Happel said, “but we have seen fish kills with contamination and sewage overflows…. There’s larger issues that aren’t bright green.”
What Do Fish Want?
Austin Happel, research biologist at the Shedd Aquarium, is tracking the movement of fish in the Chicago River. (Shedd Aquarium)
For the record, Happel didn’t design his research study to prove or disprove theories about St. Patrick’s Day shenanigans.
The real purpose is to figure out which parts of the river and its offshoots are appealing to fish and which parts aren’t.
After just a couple of years of monitoring, Happel has already noticed that fish seem to be using areas like Bubbly Creek, barge slips and canals — nooks and crannies off the main river that aren’t being managed for navigation.
“We’re trying to learn ‘how are they finding these areas?’” and what do they like about them, Happel said.
Is it the lack of boat traffic? Is the water shallower? What’s the substrate?
The ultimate aim is to pinpoint and better understand the preferred habitat, and then replicate those elements in restoration projects or provide those conditions in places where they don’t exist.
Something Fishy Is Going On
An acoustic receiver used to track fish movement in the Chicago River. (Shedd Aquarium)
Along with reams of data, Happel has also collected some excellent fish stories during the course of his research.
Like the one about the bluegill that traveled a 6- to 7-mile stretch of river multiple times a day. “I’m not sure what he was doing,” Happel said.
Or the lone walleye tagged for the project: In July 2023, it left the river for a summer vacation in Lake Michigan, came back in October, and on the same day in July 2024, left for the lake again. The lock closed before the walleye could return last fall, and Happel is keen to see if it shows up this April.
The most curious case involves a largemouth bass that pinged Happel’s array in the South Branch and on the same day, a handful of hours later, pinged colleagues’ array in the Calumet system.
“There’s no way the fish, in half a day, made it that far,” Happel said.
Putting on his detective cap, Happel learned there was a bass fishing tournament the day of the fish’s great migration. He suspects an angler caught the bass in the Chicago River and took it south to be weighed, then released it in the Calumet.
“We don’t have proof,” Happel said, but the dots are there to be connected.
It would be quite the plot twist if the same bass somehow showed up on Happel’s array again.
“We’d have our own ‘Finding Nemo,’” he said.
Contact Patty Wetli: @pattywetli | (773) 509-5623 | [email protected]
