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WATCH: Chicago River dyed green ahead of St. Patrick's Day
It's an annual tradition - large crowds gathered to watch as the Chicago River was dyed green on Saturday.
CHICAGO - Thousands of green-clad spectators gathered in downtown Chicago Saturday for the city's grand annual St. Patrick's Day celebration.
Plumbers Local 130 dyed the Chicago River a brilliant emerald green, while other boats followed to mix it in. People on the mixing boats are sponsors who paid to be there.
The Chicago tradition dates back to 1962, when local union members who were using green dye to help identify leaky pipes decided to dump 100 pounds of the dye into the river. The dye stayed there for an entire week.
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Time lapse of the dyeing of the Chicago River
The Chicago River was dyed green Saturday to kick off St. Patrick's Day celebrations!
The event has been a fixture ever since and draws thousands to downtown Chicago rain or shine.
What's in the dye itself is a "closely guarded secret,' but it's harmless to wildlife and lasts for roughly five hours, FOX 32 reports.
St. Patrick's Day is Friday, March 17.