Yep, Chicago actually turns green every March. Here's the dye-namic behind it!
Every March, the Chicago River turns green. Not just a little green, but bright, can’t-miss-it-from-the-bridge green. Crowds line the riverwalk, phones pop up, and in minutes, the water changes color right before your eyes.
It’s one of the city’s most-talked-about St. Patrick’s Day traditions, and definitely one of the most over-the-top. Celebrations like this are actually pretty rare, especially where the holiday began. “This kind of carnivalesque paddy-whackery was, and still is, generally treated with bemusement back in Ireland,” says Cian T. McMahon, PhD, a professor of history at the University of Nevada, Las Vegas, and the author of several books on Irish culture. Even so, it’s hard not to love a tradition that invites everyone—Irish or not—to join the fun.
But it does make you wonder: How does it all work, and is the green dye actually safe for the environment? Read on to find out the answers to those questions and more.
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Why does the Chicago River turn green?
For more than 60 years, Chicago has been turning its river green for St. Patrick’s Day. It all started with a plumber’s overalls. In 1961, Stephen Bailey, the business manager of the Chicago Journeymen Plumbers Local 130, noticed bright green stains on a plumber’s clothes. The dye had been used to detect leaks in the river—but Bailey, who also ran the city’s St. Patrick’s Day parade, had a thought: Why not turn the whole river green for the holiday?
The next year, with Mayor Richard J. Daley on board, the plumbers dumped 100 pounds of the same dye into the Chicago River. “It was essentially harnessing the symbolic history of the color green in a new, eye-catching way,” says McMahon. Plus, green had become shorthand for Irish identity in mid-20th-century America, so the river’s transformation resonated immediately. That first green river even earned the playful nickname “the River Shannon,” a nod to Ireland’s longest river.
While Chicago didn’t invent the idea of celebrating with green beer or green everything, its green river popularized festive traditions across the country. “Green popped up everywhere,” McMahon says. “Bars served green beer, and the Irish Social Club hosted its annual ‘Shamrocks and Shillelaghs’ dance, complete with a ‘colleen’ in green lipstick planting kisses on each male guest.”
Chicago didn’t just dye a river—it dyed the whole American imagination green (at least for the holiday).
When does the Chicago River turn green?
Every year, the Chicago River is dyed a few hours before the city’s St. Patrick’s Day Parade, which takes place on the Saturday before March 17.
The exact date changes each year (in 2026, it’s March 14), but the tradition always kicks off mid-morning. Crews release the dye around 10 a.m. local time, making the river bright green and ready for all the parade festivities.
How do they dye the Chicago River green?
In the early days, the Chicago River got its signature green from powdered fluorescein dyes, a chemical mix designed to detect leaks in pipes. By 1966, environmental concerns led the city to switch to a safer, vegetable-based dye. Today, the Chicago Plumbers Union still foots the bill and guards its more than 60-year-old secret recipe, which comes in a low-impact orange powder. Once it hits the water, it chemically transforms into a brilliant shamrock hue.
The process is a spectacle. Two motorboats work in tandem—one dumps the powder, the other stirs it—while a crew of six, including relatives of the original families who started the tradition, carefully measure out about 40 pounds of powder. It takes roughly two hours for the river to go from ordinary brown to a parade-ready emerald. It stays green for four to five hours.
And Chicago isn’t the only place showing off its Irish spirit. About an hour-and-a-half drive away, the Fox River in Northern Illinois also gets dyed green for St. Paddy’s Day.
Is the green dye in the Chicago River safe?
Yes! The Illinois Environmental Protection Agency deemed the dye “completely nontoxic,” and no environmental groups have questioned its safety. But some river advocates aren’t thrilled about the message it sends. The Friends of the Chicago River worry that turning the water bright green, even safely, can make people think the river is just a blank canvas, aka something you can dump stuff into without consequence.
“We think that dyeing the river gives the impression that it is lifeless and artificial,” the organization said in a blog post. In other words, while the tradition doesn’t harm the environment, it also doesn’t exactly scream “healthy river ecosystem” either.
Where should you go to see Chicago’s green river?
The best way to catch the Chicago River turning green on March 14 is to get to the Chicago Riverwalk early. One of the most popular spots is the walkway between Columbus Drive and State Street.
Don’t hesitate to visit in person, because, as McMahon notes, this is a tradition that can “be embraced by all Chicagoans.” So raise a glass, say “sláinte” and experience a citywide celebration you’ll never forget.
Additional reporting by Mariah Thomas.
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Sources:
- Cian T. McMahon, PhD, professor of history at the University of Nevada, Las Vegas, and author of The Global Dimensions of Irish Identity: Race, Nation, and the Popular Press; email interview, March 9, 2026
- Chicago St. Patrick’s Day Parade: “The 2025 Chicago St. Patrick’s Day Parade”
- Enjoy Illinois: “The History of Chicago River Dyeing”
- Chicago Line Cruises: “The History of Chicago and the Green River”
- Enjoy Illinois: “McHenry ShamROCKS the Fox”
- CBS Chicago: “Relatives of the men who started Chicago River dyeing tradition feel their legacy is in jeopardy”
- Friends of the Chicago River: “The impact of dyeing the river green”
- Tall Ship Windy: “The best places to watch the Chicago River dyeing”
