Cheers erupted Saturday morning as a motor boat sped around in a circle and a man on board dumped the secret dye mixture that in minutes transforms the river into a psychedelic green.
A parade will be held downtown later in the day.
This year, Ireland's prime minister is in town to help lead the celebrations.
Premier Enda Kenny appeared with Mayor Rahm Emanuel. Both wore green ties and tucked shamrocks into their lapels.
Kenny says he's honored to take part in Chicago's parade. He praised the city with a large Irish population for being so open and receptive to immigrants.
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