For more than 60 years Chicago city has been dying its river green with a "secret formula" to mark its St Patrick's Day parade and festivities, celebrated by more than 2 million people.
The tradition of dying the river began in 1962, when the local plumbers union, who still hold the honour, dyed the river green, lasting up to a month. Nowadays, it takes place on the Saturday before and lasts only a few hours.
The river was dyed green on March 11 this year, when the St Patrick's Day parade took place.
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Reuters reported on the day: "Small boats crisscrossed and poured gallons of dye into the Chicago River as part of an annual tradition marking the St. Patrick's Day holiday. Spectators along the banks of the river and on tour boats watched as the water gradually turned bright green."
The tradition started in 1961, when Stephen Bailey, who was the chairman of the Chicago Journeymen Plumbers Local Union noticed green dye on the working outfit of a plumber who was fixing leaky pipes.
Bailey, who was also chairman of the St Patrick's Day parade in the Windy City, decided to use the dye to turn the river green.
Chicago Journeymen Plumbers Local Union who were feeling festive in 1962, following permission after Bailey's request, dumped 100 pounds of green dye into the Chicago River.
Nowadays, the "environmentally friendly" dye is a well-kept secret formula, believed to be a low-impact orange powder, dispersed by two motorboats.
One spreads the dye, while the second stirs the water. A crew of six, comprised of family members from the original union members that dyed the river (Butlers and Rowans) undertake the task, Readers Digest reported.
Chicago has the largest parade in the United States, believed to be the second biggest after Dublin, dating back to 1858. Celebrations are over a week long and will continue until March 18.
Take a look above at some of the videos of the river being dyed last Saturday.
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