So THAT’S How They Turn The Chicago River Green For St Patrick’s Day… Cool.

Over 40 years ago, a plumber in the Chicago Journeymen Plumbers Union made a discovery that would change the city’s St. Patrick’s Day celebration forever. He realized that a particular dye used for water testing turned just about everything green, and he proposed that it be dumped into the river to celebrate the Irish holiday. Over the years, the dye concoction has changed and its formula remains top secret – but that doesn’t stop just about every Chicagoan from gathering around the river on Saturday to watch the entire thing go green. **If you’re outside of the Windy City this year, watch the awesome time-lapse video below.**