How Do They Dye Rivers Green for St Patrick’s Day?

St Patrick’s Day is just around the corner and across many cities, people will be seeing their rivers turn green! How does it happen? Whether related to the holiday or not, everyone likes things to be green for St. Patrick’s Day. We like to take a break from our day-to-day work life and use this as an excuse to drink, dance, wear ridiculous amounts of green and even dye our rivers!