In what year did the tradition of dyeing the Chicago River green begin? It began in 1962.
The custom grew out of an earlier plumbing investigation. Chicago plumbers used green fluorescein dye to trace illegal sewage discharges and locate pollution entering the river. The striking color gave union members the idea for a St. Patrick’s Day spectacle.
The Chicago Journeymen Plumbers Union Local 130 carried out the first celebrated river-dyeing event in 1962. The tradition became an annual fixture associated with Chicago’s downtown parade and the city’s large Irish-American community. It is generally held on the Saturday before March 17, rather than necessarily on St. Patrick’s Day itself.
A common mix-up is 1961, the year often cited for the accidental discovery that inspired the celebration. Another is the dye itself: modern crews no longer use fluorescein because of environmental concerns. They use a closely guarded formula involving powdered vegetable dye, usually described as environmentally safe and nontoxic. In 2016, the river was temporarily dyed Cubs blue for the Chicago Cubs’ World Series celebration.