At 9am on Saturday morning, the Chicago Journeymen Plumbers will change the river from a nasty shade of green into a bright, emerald shade of green in celebration of St. Patrick's Day. The dyeing has been a Chicago tradition for more than four decades, and stems from practices originally used to trace sources of illegal pollution in the waterway.
Interestingly enough, the powdered gunk that gets poured into the river to produce that glowing color is not green at all—it's actually orange. The concoction is vegetable-based, replacing the toxic fluorescein dye that the city formerly used to spot factories that were illegally dumping sewage into the river in the 1960s. According to the St. Patrick's Day Parade's website, the dye's precise recipe is "a closely guarded secret," but we're pretty sure it's just that Hi-C Ecto Cooler mix powder from our childhood.
Regardless of what kind of chemistry is at play in the orange-to-green transformation, it's pretty glorious. And if you really want to be obnoxious, you can say that the "true" Chicago St. Patrick's Day color is orange.