Chicago’s St. Patrick's Day Green River

The Chicago river dyeing is one of the most unique St. Patrick's day traditions. This typically happens the day before St. Patrick's Day at 10 a.m. and is set to be dyed again this year on Saturday. The river is dyed green by Chicago Journeymen Plumbers Local 130 of the United Association. 

This is a famous celebration that can be traced back to 1962. The tradition was supposedly inspired by an accident that happened, where plumbers used dyes to detect water leaks. In 1955, Chicago's mayor at the time, Richard Daley, wanted to know where sewage in the river was coming from. Thus, plumbers pumped green dye through the pipes to see which ones were leaking sewage into the river. According to union lore, a plumber was working with the dye and wearing white overalls when he spilled it on himself. His clothes then turned Irish green, and after reporting the incident to the union's business manager, Stephen Bailey, he called the Chicago mayor. After explaining how the water and clothes turned Irish green, Bailey proposed that since there were green streaks from running through the pipes, they could turn the whole river green by pouring the dye directly into it. He later mentioned how they should dye the Chicago River green for St. Patrick's Day.

Only a few short months later, in 1962, over a hundred pounds of dye were poured into the river, turning it green for a week. After figuring that turning it green for a week was too much, they cut back the amount and poured only 25 pounds, which lasts for only five hours. For the next few years, they kept using the same dye, only in smaller quantities. 

Until the dye was eventually found not to be environmentally friendly, and, as stated by Jennifer Wood, “Unfortunately, the dye that was intended to help spot pollution was an oil-based fluorescein that many environmentalists warned was actually damaging the river even more. After fierce lobbying, eco-minded heads prevailed, and in 1966 the parade organizers began using a powdered, vegetable-based dye.” Thus, in 1966, they switched to a more environmentally friendly dye. Ever since then, the Local 130 has refused to tell what the dye is and has only explained that it is environmentally friendly and fades after only a few hours. 

However, according to the Saint Patrick's Day Parade Committee, the dye goes in as an orange color. After it quickly turns into antifreeze, it becomes recognized as the iconic color. The Local 130 makes the joke that the transformation is thanks to a magic leprechaun. After later investigation, the dyes were found to be xanthene-based and are orange solids when dry. They are certified safe for use by the US Environmental Protection Agency and are said to biodegrade. One specific xanthene-based dye is fluorescein, which is an orange powder that turns green in alkaline conditions. However, these are all assumptions, since the Local 130 still stays silent about what the dye actually is.

Works Cited

Leigh Krietsch Boerner. “It’s Saint Patrick’s Day. Let’s Dye Stuff.” C&EN Global Enterprise, vol. 103, no. 7, 17 Mar. 2025, pp. 56–56, cen.acs.org/environment/water/s-Saint-Patricks-Day-Lets/103/i7, https://doi.org/10.1021/cen-10307-newscripts.

roneil. “Celebrate St. Patrick’s Day with Chicago’s Famous Green River.” WROK 1440 AM / 96.1 FM, 9 Mar. 2026, 1440wrok.com/st-patricks-day-chicago/. Accessed 10 Mar. 2026.

“St. Patrick’s Day Chicago: Celebrate Irish Culture | Choose Chicago.” Choose Chicago, 3 Sept. 2019, www.choosechicago.com/articles/holidays/st-patricks-day-chicago/.

Team, Digital. “Chicago St. Patrick’s Day 2026: What to Know about Parade, Green River Dyeing.” ABC7 Chicago, 9 Mar. 2026, abc7chicago.com/post/chicago-st-patricks-day-2026-pope-leo-inspired-parade-route-green-river-dyeing-where-watch-saturday-march-14/18696045/. Accessed 10 Mar. 2026.

Wood, Jennifer M. “How Do They Dye the Chicago River Green for St. Patrick’s Day?” Mental Floss, 11 Mar. 2019, www.mentalfloss.com/article/62220/what-do-they-use-dye-chicago-river-green-st-patricks-day. Accessed 10 Mar. 2026.