Chicago is full of unforgettable quirks, but few are as spectacular as the moment its river transforms into a dazzling shade of emerald green for St. Patrick’s Day. Each year, city boats glide along the waterway, releasing a special environmentally friendly dye that sweeps through the current and turns the entire river into a glowing ribbon of bright green.

Crowds gather along bridges to watch the color spread in a matter of minutes, creating a vivid, dramatic sight that feels almost magical.

This beloved tradition began in 1962 when members of the Plumbers Local Union first dyed the river in celebration of the holiday. What started as a creative idea quickly became one of Chicago’s most iconic annual spectacles, drawing visitors from around the world who come to witness the city’s bold, brilliant take on the celebration.