St. Patrick’s Day falls on a Tuesday this year, which means some of the major celebrations of the holiday took place over the weekend.
For the Windy City, that meant Saturday was the day that the Chicago River went green, an annual tradition that dates back to 1962.
The dyeing takes about five hours and involves 40 lbs. of powdered green vegetable dye going overboard from a boat as it navigates the river. (The video is soundtracked – as virtually all St. Paddy’s day-themed videos must be – to an old Irish fiddle tune called the “Kesh Jig” – you may recognize it as the basis for Flogging Molly’s “Salty Dog.”).
“You don’t have to be Irish to enjoy this,” Katherine Malhas, who was named St. Patrick’s Day Queen in 1970, told the Chicago Tribune. “It’s a Chicago city celebration.”
And it just wouldn’t be St. Patrick’s Day without it.
Read next: How America Invented St. Patrick’s Day