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.
Here you see the boats holding the dye waiting for the go-ahead. Note the crowds lined up to watch. 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
