As to how Chicago dyes its river green, this started back in 1962 when Chicago Plumbers Union business manager Stephen Bailey got the idea to use a dye for tracing leaks in buildings to bring the river into the celebration. The Chicago Plumbers Union has been doing it ever since, using a powdered dye with a secret recipe that's similar to food coloring.
This year they dumped around 40 pounds of dye into the river, and it should last between 24 and 48 hours. This is actually the largest stretch of river the city has ever dyed, stretching out to State Street, which means hundreds more people watching from the four bridges with a view of the river.
Plus you watching this time-lapse again because it's super-cool.