St. Patrick's Day tradition: Why Chicago dyes its river green and is it harmful?

ByScottie Andrew, CNN
Thursday, March 17, 2022
Timelapse of Chicago River being dyed green
Chopper 7 HD flew over the Chicago River as it was dyed green for St. Patrick's Day in 2022.

CHICAGO -- For the last 60 years, enterprising Chicagoans have dyed the city's river a vibrant green in honor of St. Patrick's Day. Thousands of residents turn up to watch the Chicago River light up for the holiday, a tradition so popular it's inspired cities nationwide to color their own waterways.

This year's celebrations were a welcome return to form for Chicago, which canceled previous St. Patrick's Day parades due to the pandemic. Read on to learn more about the tradition, its union roots and the dye so secret only a select few know the recipe.

The tradition was started by plumbers

In the 1960s, Chicago city workers used a bright green dye to identify leaks in pipes, which would often stain their white coveralls, CNN reported in 2019. In 1962, members of the Chicago Journeymen Plumbers Local Union who were feeling festive dumped 100 pounds of that dye into the Chicago River, which turned it green for an entire week, per the Illinois Office of Tourism.

The union has since perfected its viridescent formula, and these days, it only dyes Chicago's waterways for a few hours on a Saturday on or before St. Patrick's Day, when Chicago's St. Patrick's Day Parade is held.

A crew of six dyes the river

The dyeing process itself is surprisingly simple: It takes just two boats, each featuring relatives of the first families to dye the river -- one boat does the dumping, and the other does the mixing.

Around 40 pounds of dye and two hours later, the six-man team successfully turns the river a shade of shamrock green. And though the dye only lasts a few hours in the river, it stains the fingernails of the the small but mighty team for weeks.

The dye is vegetable-based

Unsurprisingly, the chemical-laden dye initially used to color the river was doing more harm than good, and in 1966, environmentalists convinced the city to adopt a formula made from vegetables, according to Mental Floss.

The recipe itself is a closely guarded secret -- all we know is that it's an orange powder that turns green in the river. Residents pin the magical color change on leprechauns, naturally.

It's inspired copycats

Though Chicago's green river is arguably the most famous in the US, other cities have concocted their own dyes for their local waterways, from Savannah, Georgia, where a historic fountain spews green, to San Antonio, Texas, which dyes its picturesque river while a bagpiper plays. But nothing beats the original spectacle in Chicago -- after all, it's got leprechauns on its side.

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