Is the Chicago River Dye Eco-Friendly? Everything to Know About This Decades-Old Tradition

Every March, cities nationwide gear up for their annual St. Patrick's Day celebrations — including Chicago, which annually dyes its river green. In addition to hosting parties citywide, the Windy City's "green river" is a festive phenomenon which attracts thousands of visitors every year.

But because rivers in the U.S. are notorious for ecological destruction, we can't help but wonder what the Chicago River is dyed with. Is it safe? Here's what you need to know about this tradition and what the Chicago community thinks about it.

"The dye used is a food grade dye also used in medicine, as the colorant for antifreeze and as a tracer dye. The Illinois EPA found that at the concentration used in the Chicago River, it is completely non-toxic," reads a statement from the EPA, as per NiCHE Canada.

"We didn’t do a lab test on a sample of the dye [intended for the Chicago River]. EPA contacted the Plumbers Unions on what was in the dye. Then, EPA’s toxicologist reviewed the dye’s ingredient and deemed it safe.”

According to the Chicago Sun Times, the Chicago River has been dyed for several years by the Chicago Plumbers Union Local 130, specifically, by two families: the Rowans and the Butlers. The families have kept the powder mix recipe, known as "Leprechaun dust," a secret for many years.

In 1962, former Chicago Mayor Richard Daley proposed a large-scale celebration for St. Patrick's Day. Per the Chicago Sun Times, Daley and a friend, Stephen Bailey from the Plumbers Union, brainstormed dyeing Lake Michigan, but when that seemed too big a task, they settled for dyeing the river instead.

Initially the dye, which used to be made of fluorescein, was used to test leaky pipes, and it would last for a week. Environmentalists have since identified environmental issues behind using oil-based fluorescein in a natural body of water, so in 1966, the plumbers union transitioned to using what's used currently: a low-impact orange powder that's made from vegetables. The mixture turns green as soon as it hits the water, and lasts for 48 hours.

NiCHE Canada's Isaac Green says the green tradition has a negative undertone.

"Dyeing the river continues and perpetuates the notion that we can modify rivers to suit our tastes with no regard to the consequences. Thus, even if the dye itself isn’t ecologically harmful, the process of dying the river can sustain harmful ecological ideas," Green writes. "... the dye allows people to believe the river isn’t 'natural,' therefore justifying its treatment as a sewer."

Additionally, multiple environmental groups have pushed back against dyeing the river. In 2021, Friends of the Chicago River, Openlands and the Illinois Chapter of the Sierra Club wrote an open letter to the Chicago Sun-Times explaining that when the tradition began in 1962, the Chicago River was all but dead. Since then, it has been revitalized, which means the dye could cause greater harm to the ecosystem that now resides within.

Environmentalists also worry that even though dyeing the river green is low-impact, it could influence people to dump whatever they want into the river, essentially using it as a "trash can."

Sometimes rogue Chicagoans participate in illegal dyeing — when the tradition was called off due to COVID in 2020, according to Euro News, many got in trouble for dumping their own green dye into the river. Likewise, this sometimes happens in other parts of the river, because only the stretch downtown is allowed to be dyed. Since the vegetable mixture used to dye the river is a secret recipe, the illegally-dumped dye may not be as eco-friendly.

This article, originally published on March 15, 2022, has been updated.