From the March 13, 2015, Chicago Tribune according to Tom Rowan, head of the crew that does it.
Earlier today, the Chicago River downtown turned into a shocking hue of green as part of a long-standing tradition.
The event dates back to 1962, when Mayor Richard J. Daley and Stephen Bailey, a boyhood friend and the St. Patrick's Day parade chairman, started the tradition. At 9:15 a.m. Saturday, the river will become a bright green again. Here's how the process works, and where to watch the dye job.
1. PREP WORK: Early in te morning, the crew arrives at a city boat slip on the North Branch of the Chicago River. Everyone wears clothes and shoes they don't mind getting dirty and a white paper smock over their clothes.
2. ON THE WATER: The crew hops aboard two small motor boats donated by volunteers. The larger boat, at approximately 18-feet, has a crew of four. The smaller boat, a 12-footer, has two people.
Put Some Green in My River. --RoadDog