One asks oneself certain questions in 2012 (even we Irish and part-Irish). But apparently, this was answered long ago. Erin go Bragh!
In 1966, the environmentalists accused the parade committee of polluting the river. They complained that the dye was oil-based and was detrimental to all living things.
Bailey laughed when he heard their argument but agreed to find a new compound that would do the job and appease the critics.
The committee experimented with a number of vegetable dyes and after a bit of trial and error, the current 40 lbs of new dye was hit upon. It produces a carpet of green for four or five hours. The flamboyant Bailey had a field-day with the press when he announced he was changing the Chicago River to the Shannon River for one day.