How long does the river stay green? – NBC Chicago

The Chicago River was dyed green on March 15, 2025, as part of the city’s iconic St. Patrick’s Day tradition, with the color expected to last for a few hours and possibly for days. The Plumbers union used a secret orange dye mixture that turns green once in the water, a tradition that began in 1961 and remains a closely guarded secret. The dyeing process takes place either the weekend before or after St. Patrick’s Day, with the river maintaining its emerald color for several days after the initial dyeing.

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