For six decades, Chicago has marked St. Patrick’s Day by dyeing the river bright green, with the color lasting for a couple of days. It’s just one part of the city’s festive celebrations. But where did this tradition come from?

The history of St. Patrick’s Day celebrations in Chicago date back to more than 175 years ago, according to Choose Chicago . Experiencing the holiday in the windy city has become a bucket list item for many.

Though Chicago is known for dyeing the waterway that runs through the city green since 1962, the tradition did not begin as an act of celebration. Instead, the dye was a part of the city’s plan to clean the waterfront areas, “which had long been a depository for Chicago’s waste,” according to NPR . The green dye was used to pinpoint where the waste was coming from.

This led to Richard J. Daley, the mayor of Chicago in 1955, to the idea of dyeing a part of Lake Michigan green to commemorate St. Patrick’s Day. His friend, Stephen M. Bailey, business manager of the Chicago Plumbers Union, convinced him to dye the Chicago River instead, due to it being a more manageable size, per the article .

The original dye that was used in the attempt to clean Chicago was oil-based. Since then, it has been changed to an orange powder which turns green once mixed into the river. The city has kept the formula of the dye locked down in secrecy.

“Illinois EPA has never required a National Pollutant Discharge Elimination System (NPDES) permit so there is no way to know what the dye is or whether it is harmless,” Margaret Frisbie, executive director of Friends of the Chicago River, said in a statement to NPR .

The city has experimented with different ways to distribute the dye throughout the river. Once, they used fire extinguishers. This not-so-bright idea instead covered the Wrigley Building and over 100 cars in the city in the orange powder, Chicago Alderman Edward Burke told NPR .

Chicago found a solution that works — two motorboats. One of the motorboats dumps in the powder while the other one stirs the water to mix in the solution evenly.

Other St. Patrick’s Day celebrations in the city of Chicago

Parades

This year marks the 70th anniversary for the annual Chicago St. Patrick’s Day Parade — one of the largest in the country, according to Choose Chicago .

The parade takes place on Columbus Drive from Balbo Drive to Monroe Drive, per the website.

The parade is a festive opportunity to experience The Shannon Rovers Irish Pipe Band which has been a main feature of the event since the first official parade in 1956.

The celebrators can also attend the South Side Irish Parade and the Northwest Side Irish Parade.

River cruises

Those who are most excited about witnessing the bright green river can experience it while floating down the river directly on an iconic Chicago river cruise.

Some of the cruises offer Irish cuisine to enjoy while you float down the river to the sound of bagpipes playing in the background, per Choose Chicago .

Neighborhood festivities

Along with the parades, dyeing of the river and river cruises, St. Patrick’s Day celebrators can visit the Irish American Heritage Center , which will have a variety of activities and events.

Visitors can attend an Irish singing workshop and Celtic art classes among other activities.