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March 11, 2023

Chicago dyes its river green every year for St Patrick's Day

As Chicago's St Patrick's Day parade made its way through the city on 11 March (St Patrick's day in the US), it was met with a slightly odd sight: a stretch of the Chicago River glowing a bright, chemical green. 

By City Monitor Staff

For more than 50 years now, Chicago has dyed the river green to mark St Patrick’s Day and decorate the route of its annual parade. For long-time residents, the sight is now pretty commonplace.

st patrick's day
People view the Chicago River after it was dyed green in celebration of St Patrick’s Day. (Photo by Scott Olson/Getty Images)

Chicago is renowned for its annual St Patrick’s Day parade

The tradition of dyeing the river green for St Patrick’s Day has been a part of the city’s festivities since 1962 and has become an annual event for locals and visitors alike. The tradition began when the city’s Irish population wanted to honour their heritage.

The St Patrick’s Day tradition of dyeing the river, however, actually started as an accident: plumbers used a type of fluorescent dye to trace the source of pollution in the river, but then realised that the bright green colour could be used to mark St Patrick’s Day.

The dyeing is sponsored by the Plumber’s Association to this day, and every year two boats set out to distribute the dye an hour before the parade starts.

The dye is now made from environmentally friendly vegetable dye, which is applied to the river with a barge. The dye used in the river is non-toxic and safe for the environment. It is also harmless to humans and animals, making it a safe way to celebrate the holiday, but swimming is still not advised, of course.

The dye is visible for up to five hours on St Patrick’s Day, but it can take up to eight hours for the dye to completely disperse.

The event is also great for local businesses as it brings in many visitors to the area for the celebration. So move over, Boston.

So, if you’re ever in the area on St Patrick’s Day, don’t forget to check out the electric green river. Though that is likely the whole reason you went there…

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