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18th March 2014
04:17pm GMT

The Chicago River has been dyed every St Patrick's Day by the city's plumbers union as a privately funded operation for the past 52 years. Volunteers hopped on to motorboats with containers of a "secret formula" and painted the river a bright shade of emerald green.
The river usually remains a bright shade of green between six and 12 hours.
See the Chicago River going green in this great time lapse video below:
We think it's pretty cool.