Watch: Time-lapse shows the Chicago River turning green for St. Patrick’s Day

St. Patrick’s Day celebrations have officially kicked off in Chicago, and the party started with the dyeing of the Chicago River on Saturday.

The iconic event takes place on the Saturday prior to St. Patrick’s Day, with the Chicago Plumbers union putting a special dye into the river to give it an emerald green color.

Thousands of residents turned out for Saturday’s river dyeing, which takes around 45 minutes to an hour to complete.

Fortunately for our viewers, we have a time-lapse that shows the entire process in a matter of seconds, with the river taking on its distinctive hue in just 30 seconds.

As the 2026 river dye celebration wraps up, take another look at the moment the Chicago River transformed into its iconic bright green color.

The story of the Chicago River being dyed green began with a happy accident. A man by the name of Stephen Bailey — the business manager of the plumbers union — was approached by “one of his plumbers who was wearing some white coveralls,” a post by Local 130 says. It was then the union says, that Bailey noticed the overalls had been stained or dyed with “a perfect shade of green,” or “an Irish green to better describe it.”

When wondering how the coveralls could have turned such a tint, the tale continues, Bailey and his plumbers discovered that it was from to the dye used to detect leaks in the river.

Originally the idea was floated to use the dye to turn Lake Michigan green, but the ambition was tempered slightly and was turned to the river instead.

The recipe of the dye is a closely guarded secret, but city officials always emphasize that it is environmentally friendly.