Dyeing the river itself is a pretty straightforward and simple process that only takes 45 minutes.  A crew arrives in the morning on the edge of the river wearing smocks and ragged clothes with two small motorboats and one larger boat with about 45 pounds of dye on hand. Once they take off, three men sift the powder into the river at once while the smaller boats drive behind and stir the water to ensure that it is evenly dispersed in the river. Just like that, the murky waters turn into a work of art.

For more than 40 years, members of the Chicago Journeymen Plumbers union have turned the river a bright emerald green by dumping a secret concoction off the sides of their motorboats. The city says it takes more than 45 pounds of the environmentally friendly vegetable dye to color the water, using a powdered formula that begins orange before it mixes with the water to turn the river bright green. It typically lasts about five hours before fading away.

From now on when you pass the green Chicago River, you can tell everyone how it’s made!