I have lived in or next to the city of Chicago my whole life and have NEVER seen the Chicago River dyed green for Saint Patricks Day until this year (it has been going on for 43 years and by the way, these photographs of the river have not been altered at all...this was the true color of the river). It was quite a spectacle.
You could feel the excitement in the air. Everyone was smiling and wearing shades of "Irish" green. The idea to dye the river green came about by accident when a group of plumbers were using fluorescein dye to trace illegal substances that were polluting the river. They EPA eventually outlawed the use of fluorescein for this purpose, since it was proven to be harmful to the river. Now, 40 lbs of a vegetable dye is used to produce a carpet of green for 4-5 hours, claimed safe to the thousands of living organisms that find a habitat in the Chicago river.
HAPPY ST. PATRICKS DAY!