The Chicago River is a system of rivers and canals with a combined length of 156 miles that runs through the city of Chicago, including the Chicago Loop. Though not especially long, the river is notable because it is one of the reasons for Chicago's geographic importance: the related Chicago Portage is a link between the Great Lakes and the Mississippi River Basin, and ultimately the Gulf of Mexico. The Chicago Plumbers Union Local 130 is responsible for the famed St. Patty's dyeing of the River (which will last for 24 to 48 hours). They turn the Chicago River green with a proprietary dye in three boats: two with the secret sauce and a chaser vessel to mix it up. The pigment is basically food coloring that plumbers invented years ago to help them track down leaks! In this classic image by Morgan, the vibrant green dye is long gone, and we see the river in all its glory, shrouded in city.