Answer: Plumbers

For decades the city of Chicago has dyed the Chicago River green to celebrate Saint Patrick’s Day, but the idea didn’t just come out of thin air, it was inspired by the work of city sanitation workers and the vision of a plumber in the right place at the right time.

During the early part of Richard J. Daley’s stint as an influential mid-20th century mayor of Chicago, he supported and pushed through serious redevelopment projects along the Chicago River. Part of the process involved cleaning up the water itself and identifying who was illegally dumping waste into the river. To that end, city workers seeded drains and sewers with green dye and then combed the river looking for places the should-be-contained waste was leaking out into the river.

This effort and technique went on for years, but in 1961 Stephen Bailey, plumber and chairman of the Saint Patrick’s Day Parade committee, saw the dye in the river and had a very grand idea: he could put the Chicago Saint Patrick’s Day celebration on the national map by dying the whole river green. With approval from the city and a huge amount of dye, he dyed the entire river green for the 1962 parade.

Years later the tradition lives on with a minor modification. The original recipe called for 100 pounds of a dye that was later shown to be toxic (and dyed the river green for upwards of a week). Today a green non-toxic dye is used and the spectacle only lasts for 4-5 hours.