They dye the Chicago River green for St. Patrick’s Day by dropping a special, plant-based orange powder into the water from small boats, which turns bright green as it mixes and spreads through the current.

How Do They Make the River Green in Chicago?

Quick Scoop

For St. Patrick’s Day, a crew from the Chicago Journeymen Plumbers Local Union 130 rides motorboats along a downtown stretch of the river and tosses in an orange , vegetable-based dye that turns green on contact with the water. They use roughly 40–60 pounds of this environmentally safe, plant-based powder to create the famous emerald color that usually lasts several hours.

How the Dyeing Actually Works

  • Plumbers union members load onto a couple of small boats early in the morning on the Saturday closest to St. Patrick’s Day.
  • From the boats, they shake or spray the orange powder into the river as they move along a short downtown section (roughly a quarter mile between key bridges).
  • As the powder hits the water, a chemical reaction with the river’s color and light makes it appear a vivid green within minutes.
  • The color is brightest in the late morning and then gradually fades over the course of the day.

Think of it like stirring food coloring into a big pot of water, except the “coloring” starts out orange and only turns green once it meets the river.

What’s in the Dye (and Is It Safe?)

  • The formula is a closely guarded secret, sometimes jokingly called “leprechaun dust.”
  • Organizers describe it as plant-based, vegetable-derived, and non-toxic, designed to be safe for people and the environment.
  • Only a relatively small amount (around 40–60 pounds) is needed to color the large visible stretch, because the current helps distribute it quickly.

Some local environmental groups still criticize the tradition symbolically, arguing the river should be treated more as a living habitat than a backdrop for stunts, even if the dye itself is considered safe.

A Quick Bit of History

  • The tradition started in the early 1960s, when plumbers used a similar dye to trace illegal sewage leaks and noticed how dramatically it colored the water.
  • Chicago’s then-mayor Richard J. Daley originally liked the idea of dyeing Lake Michigan but settled on the more manageable Chicago River.
  • The first official green river for St. Patrick’s Day happened in 1962, and it has been a yearly ritual ever since (barring a few unusual years).

Today, it’s one of the city’s most recognizable March events, drawing hundreds of thousands of spectators to watch the river turn that intense St. Paddy’s green.

When It Happens and What It Looks Like

  • The river is typically dyed on the Saturday before St. Patrick’s Day, starting around 10:00 a.m. local time.
  • The boat passes and dye application take roughly 45–60 minutes, but the bright green effect sticks around for several hours afterward.
  • Best viewing spots are downtown bridges and the Riverwalk, where you can watch the boats “draw” bright green swirls that blend into one continuous emerald ribbon.

TL;DR:
They make the Chicago River green by having the plumbers union boat along the river and toss in about 40–60 pounds of a secret, plant-based orange powder that turns the water a bright, temporary, environmentally safe green for St. Patrick’s Day.

Information gathered from public forums or data available on the internet and portrayed here.