- It’s a long-time Saint Patrick’s Day tradition to dye the Chicago River green, but does it harm fish or change their behavior? As far as scientists can tell, the answer to those questions is no.
- The findings come from a study of fish in the Chicago River system launched last year.
- Researchers are tracking the aquatic activity of more than 80 fish they’ve tagged for study.
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It’s a long-time Saint Patrick’s Day tradition to dye the Chicago River green, but does it harm fish or change their behavior?
As far as scientists can tell, the answer to those questions is no.
How do they know?
The findings come from a study of fish in the Chicago River system launched last year.
Researchers are tracking the aquatic activity of more than 80 fish they have tagged for study.
During last year’s parade, scientists say none of the tagged fish sought shelter as the water turned green, suggesting it is not impacting their daily habits or harming them.
How do they monitor the fish?
Biologists can detect movements by the fish through acoustic receivers placed in various parts of the waterway, allowing them to learn how fish respond to habitat restoration, flooding, sewage overflows and seasonal changes.
Why are environmentalists concerned?
The dyeing of the river has concerned environmentalists since its inauguration in 1962, in which oil-based dye kept the water green for nearly a month. Since then, a vegetable dye, which the Illinois Environmental Protection Agency says is nontoxic to wildlife, has been used.
Researchers now say the tagged fish appear to be unbothered by the dye, but other things like heavy rain and wastewater overflows lead them to escape to areas where oxygen levels aren’t depleted.
If fish are unable to leave a contaminated environment, it often kills them in massive numbers over a very short period of time.
Researchers said they have yet to witness any fish killed from the dye.
How is the biodiversity along the river?
The group also says that the river is the healthiest it has been in the past 150 years, with all kinds of wildlife, including birds, turtles, beavers and more than 80 species of fish in and around the river’s waters. Those 80 species are up from fewer than 10 species of fish in the 1970s.
Why are environmentalists still opposed to the tradition?
Despite the findings, environmentalists still question whether dyeing the river is the best example of being good stewards of the Earth, and many remain opposed to the tradition.
