How Chicago Dyes Its River Bright Green For St Patrick's Day

While the rest of us are chugging pints of Guinness with the Irish flag drunkenly draped around our shoulders, the city of Chicago likes to go BIG when it comes to St Patrick’s Day – famously dying its river bright green every year. 

Each time March rolls around, the Chicago River becomes such a luminous shade of green the stunt looks like a viral hoax, but it's actually a tradition that the Illinois city has been honouring since the 1960s. It all began when Mayor of Chicago Richard J Daley was trying to do something about the sewage-filled river, and decided to pour a special green dye into it to try and pinpoint the exact locations where waste was being dumped from leaking pipes. It was this that led to the lightbulb moment, as people wondered if the same idea could be applied not just to sections of the waterway, but to the whole thing. 

Chicagoan Bob Rowan – who has worked behind the scenes of the annual stunt for more than a decade, although his family have been involved for much longer – recalled to Marriot Bonvoy Traveler: ‘The story goes that there were some plumbers who spilled green dye into the water, and when Mayor Daley Senior saw it, he wanted to know if we could do it for St. Patrick’s Day – he was a big St. Patrick’s Day guy.’ 

The mayor went to Rowan’s father Tom, who was in charge of the river’s police boats at the time, and asked if he could help. 

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‘The mayor’s office went straight to him to talk about it, and we’ve been dyeing the river ever since,’ Rowan said, having seen his brother Thomas take on the job when their father passed away in 2002, before joining in himself in 2005. 

Originally, the dye used was an oil-based fluorescein, which was often used at the time to detect leaks. However, after concerns from environmentalists that it was toxic to the river, the team changed to a powdered vegetable-based dye from 1966. 

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Nowadays, the dyeing process kicks off at 9.00am on the morning of the parade, which takes place each year on the Saturday before St Patrick’s Day. Members of the Chicago Plumbers Union use two boats to distribute the dye, with the larger vessel heading out first to spread it into the water with large hoses controlled by the crew. The smaller boat then follows behind to help disperse the dye around the water, before the river is fully green just 45 minutes later. 

According to Chicago Line Cruises, in 1962 the team poured 100lbs of dye into the river to turn it green for a week, but over the years experimented with the ratios – today using 40lbs of the environmentally friendly substance to colour the river for four to five hours.

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'We’ve practiced a long time to get it right,' Rowan said. 

'It’s not that easy to land on the perfect shade of green without big giant streaks in it, and it’s taken us quite a few years to figure out how to do that – but now we have a way of putting it down so it comes out evenly and in a nice, bright hue.' 

He explained there are a number of variables that need to align for the full effect to take place, including the weather.

‘We did it one year when it was real windy, and the dye blew up onto Wacker Drive, so we ended up dyeing the entire South Side of Upper Wacker green,' Rowan said.

'As I passed people on the street and saw the green all over their faces, I was like, 'We need to get out of here'. It was pretty wild.’ 

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The water needs to be pretty clear, too, with Rowan admitting they once tried the stunt in Dublin, Ireland, but that the river was simply too murky for it to work properly. 

'When we arrived we were given a tugboat – it was so huge it was comical,' he said. 

'What’s more – the river was so dirty that it barely turned green.'

Thanks to the Covid pandemic, Chicago hasn't been able to celebrate St Patrick's Day as it normally would for the past two years; the famous parade was cancelled for 2020 and 2021, although crews still dyed the river last year as a surprise to locals after a hiatus the year before. However, the spectacle made its triumphant return last weekend on March 12, with crowds gathering along the river bank to see the display in action.

Speaking to the Chicago Sun Times, resident Ozzy Arias said: 'It’s cool seeing everybody back out, everybody having a good time – a lot of smiles. It’s a beautiful thing when everybody gets back out together with a group of friends.'