The St Paddy’s Day river dyeing is a fun tradition for Chicagoans and tourists alike, but where did it begin?

Years prior to today’s beautiful riverfront paths and the many kayak tours, the river was polluted with sewage water. Mayor Daley realized no one wanted to live next to a contaminated waterway, so he began cleaning it up. According to Chicago Mag, the city’s plumbers did this by putting some “green dye into the city’s waste systems to trace the flow of waste discharges”.

After the smears of green started appearing in the water, they got the idea to turn the entire thing green. The first time they tried it with a large batch, the river was green for almost a week. After a few years of trial and error, they finally got the amount right – and thus, the yearly day of radioactive-looking water was born in 1962.

The irony of all this?
The original formula was an oil-based fluorescein – meaning the substance that was originally used to help efforts to clean up the river, was actually super damaging for water. They switched the formula in 1966 after environmentalists lobbied to stop the use of it. Don\’t worry, the tradition still lived on; they just switched to a vegetable-based dye in powder form.

So what exactly is in this power?
NO ONE KNOWS! The Plumbers Union refuses to reveal the trademark formula. Part of me is disturbed by this (what the heck are they dumping into our drinking water?!), and the other part thinks it\’s like a secret recipe, akin to Olive Garden breadsticks.

For the first part, major environmental groups aren\’t actively opposed to it, so it\’s probably pretty harmless. But for the second…seriously, how are those breadsticks so delicious?!

For a more in-depth look at the river-dyeing, read these articles from Chicago Tribune, Mental Floss, and Chicago Mag.