A Chicago resident has turned the seemingly complex task of turning an entire river in a major U.S. city green for St. Patrick's Day into a 30-second task.

Peter Tsai posted a time-lapse video to YouTube showing how the Chicago River in his hometown is dyed emerald green in a generations-long tradition.

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The 30-second video shows boats dripping containers of dye into the river as city life goes on as normal around them.

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The Chicago Journeymen Plumbs Union Local 130 dumped the dye - the recipe for which only they know - into the river beginning around 9:30 a.m. Saturday, ABC News station WLS-TV in Chicago reported.

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The dyeing of the river has been a tradition in the city since 1962, according to WLS. It led up to the city's annual St. Patrick's Day Parade, which was also held Saturday and attracted a crowd estimated at nearly 1 million people.

The river's green hue typically lasts about six to 12 hours.