Mesmerize Yourself With This Time-lapse Video of the Chicago River Going Green for St. Patrick’s Day

image via youtube screen capture

There’s something hypnotically soothing about seeing the Chicago River slowly turn a vivid shade of Kelly green to celebrate St. Patrick’s day; it’s like watching a gigantic lava lamp undulate through the heart of downtown Chicago.

The tradition of dying the Chicago River in honor of St. Patrick’s Day dates back over fifty years, and is something of a local legend. As the story goes, in an attempt to trace illegal pollution seeping into their water, a team of local plumbers used the chemical fluorescein to track the contaminant’s source. After noticing their efforts had turned the water green, they brought up the idea to deliberately color the river—though some say they’d originally set their sites on Lake Michigan—for the Irish holiday. Once permission was granted by then-Mayor Richard J. Daley, a tradition was born. To this day, the task of dying the river remains in the hands of the Chicago Plumbers Union.

Today’s green hue comes from a proprietary mix of over 40 pounds of eco-friendly vegetable dye, a switch made after the Environmental Protection Agency declared fluorescein itself a potential hazard to the water. Once a series of boats mix the dye into the river, the neon hue is set to last anywhere from a few hours to several days (depending on the wind) before the water reverts to its ordinary, non-celebratory murky green color.