How much dye does it take to turn the Chicago River green?

While it varies from year to year, it typically takes at least 40 pounds of dye to turn the Chicago River green for St. Patrick's Day. Local plumbers have dyed the river every year since 1961, and in the early days they used nearly 100 pounds of coloring, which left the river green for days after the celebration.

The reduced amount of dye used in more modern celebrations ensures the water returns to a normal color more quickly. The river's shocking shade of green comes from the same vegetable-based dye that's used to detect cracks in the city's sewer system.