Chicago River Runs Green on St. Patrick's Day

If your not from Chicago you may not know that every year on St. Patty's Day The Chicago Journeymen Plumbers dye the River Green. Really Green, but the dye they use is actually orange when they put it in the River

Here's a link to cool article in the Christian Science Monitor about the history and process of why this has become a Chicago Tradition on St. Patricks Day.