Every year Chicago dyes the Chicago River green in celebration of St. Patrick's Day. See how they do it in this step-by-step photo tour.
The boats go back and forth along the river spilling more dye and stirring up the water. Learn more about the history of this Chicago tradition, where and when it takes place, and what environmentalists have to say about it.
Related: Chicago St. Patrick's Day - Events, Traditions, History | Downtown St. Patrick's Day Parade