The beloved tradition almost never happened.
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Chicago River
Credit: Scott Olson/Getty Images

While St. Patrick's Day in Chicago will be celebrated with a parade on Thursday, every year, preparations begin on the Saturday before the holiday as the city turns its namesake river green — a decades-long tradition that almost never happened.

In 1961, the city of Savannah, Ga. tried to dye the river behind its City Hall green, however, the best it could do was create colored streaks in the water. The following year, Mayor Richard J. Daley — a politician of Irish-American descent who was raised in a heavily Irish neighborhood in Chicago — had been hoping to turn Lake Michigan green for the holiday.

Soon finding out that turning Lake Michigan green was a bit too much to ask, a group of Chicago plumbers identified the right formula for turning a city river the perfect shamrock shade, and a new holiday tradition was born. And finding the perfect shade was truly a happy accident as the plumbers union's business manager noticed bright green stains on another worker's coveralls while on a different job, according to Ilinois's tourism site.

"The dying of the river green is such a public event that it helped concretize the celebration of St. Patrick's day in the city," Peter Alter, chief historian at the Chicago History Museum, told Travel + Leisure.

Had Daley not been of Irish heritage, Alter said, St. Patrick's day may not have become a marquee city holiday.

That first year, the Chicago Journeyman Plumbers Union dumped 100 pounds of dye into the river, turning it green for a solid week. Nowadays, the union uses about 40 pounds of vegetable-based powder dyes that are more environmentally friendly and turn the river green for just a few days. 

The hue can last for days, depending on the weather. Every year, thousands of people brave the early morning cold to catch a glimpse of boats dropping dye into the river before the city's parade begins its march through downtown.

"It's the perfect storm of celebration," Alter said. 

Chicago is one of several U.S. cities that drew large numbers of Irish immigrants in the 1800s. By 1850, about one-fifth of the city's population was Irish and what had been an unofficial parade became an official city celebration of Irish heritage that would grow into a legendary place to spend March 17. 

Chicago River
Credit: Scott Olson/Getty Images

In addition to the city's main St. Patrick's Day parade downtown, parades are held on Chicago's South Side, a hub for its Irish population, and in Norwood Park, a northern neighborhood near Chicago O'Hare International Airport. 

Last year, amid the COVID-19 pandemic, the tradition of turning the Chicago River green still occurred, but spectators were encouraged to enjoy the view while socially distancing.

Meena Thiruvengadam loves wandering new streets and discovering the world's stories. Subscribe to her newsletter, and look for her on Facebook and Instagram.