Chicago's River Runs Green for St. Patrick's Day

It's St. Patrick's Day in Chicago, and the city's iconic river is glowing green again.

Members of the Chicago Plumbers Union are behind the transformation each year, deploying a fleet of boats, including riverboats carrying spectators, to spray a specially mixed dye directly into the water through plumbing pipes and spout pumps. The mixture actually comes out orange at first, then quickly shifts to a vivid green as the dye sets into the water, a process originally developed by plumbers to detect leaks in broken pipes.

The brilliant green color lasts only a few hours, though the river stays tinged for days before slowly fading.

The dyeing is just one piece of Chicago's St. Patrick's Day celebrations. The city also hosts the downtown St. Patrick's Day Parade, the Northwest Side Irish Parade, and the South Side Irish Parade, which officials say is the largest community-based St. Patrick's Day parade outside of Dublin, Ireland.