Color Us Surprised! Learn Exactly How the Chicago River Turns Green for St. Patrick's Day

Chicago’s homage to St. Paddy’s Day has a storied history and a secret formula.

St. Patrick’s Day is always a fun holiday, whether you’re Irish or not. With its signature green hue, the holiday has even taken to the waters of several rivers across the United States as a sign of celebration, with Chicago being the most famous one of all. Dyed to create even more festive ambiance for the city’s 180-year-old parade, people gather in droves (a whopping 400,000!) to see the team of six transform the river from its usual color to a kaleidoscopic emerald shade. Spectators will even take to tour boats and kayaks to get an up-close look at the lime-green waters.

While cities like Washington, D.C., San Antonio and Indianapolis also give their rivers the Kermit-the-Frog treatment, Chicago is undoubtedly the most well-known since it attracts so many onlookers and has been taking place for six decades. But, like the rest of us, you may have some questions as you ponder this green-dyed wonder.

For instance, what exactly is that dye that’s used to turn the river green? Who does it? How long does the river continue to stay green? Does it stay green for days, or even weeks? What’s the history? And is it harmful to people and to the wildlife that swim its waters?

Ahead, we’ll answer all these questions and more.

Related: 20+ Family-Friendly Activities To Get Your Teaghlach Into the Spirit of St. Patrick’s Day

When Will Chicago Dye Its River Green in 2023?

The Chicago River will be transformed into a green hue on Saturday, March 11 at 10 a.m. CST—immediately before their St. Patrick's Day parade. With St. Patrick's Day on a Friday this year, it makes sense to have the festivities the weekend beforehand.

How To See the Green Chicago River

While some spectators will be lucky enough to see the infamous green water in person, ABC7 will also be streaming Chicago's St. Patrick's Day Parade starting at 12:30 p.m. CST.

What Does Chicago Use To Dye the River Green?

Well, that’s a secret, actually! The green dye, with ingredients that are kept hush-hush, is said to be an orange-red, vegetable-based powder. Originally, a chemical-heavy plumber’s dye was used, but then in 1966, environmentalists petitioned the city to switch to something more eco-friendly, and that’s when the vegetable dye came in.

Who Turns the Chicago River Green?

It’s the Chicago Journeymen Plumbers Local Union 130 (bet you weren’t expecting that!), and all it takes is 50 pounds of dye, a couple of motorboats and 45 minutes to turn a portion of the 156-mile Chicago River green. Relatives of the very first people to dye the river still participate to this day. The water is dyed just a few short hours before Chicago’s annual St. Patrick’s Day parade to create a truly celebratory atmosphere.

Related: 12 St. Patrick's Day Party Cocktails and Appetizer Ideas for the Most Irish Day of the Year

How Long Does Chicago Keep the River Green?

With that bright, saturated shade of green, it might seem as if the Chicago River will stay green forever! But that’s not the case—it begins going back to its usual hue after 24 to 48 hours. This is a far cry from the 100 pounds of dye that was originally dumped into the river in 1962, which caused it to stay green for an entire week.

Related: Get Lucky This St. Patrick’s Day with 25+ Do-It-Yourself Crafts for Preschoolers, Tweens & Teens!

How Long Has Chicago Been Turning the River Green?

Much like Ireland’s vibrant history, the background of turning the Chicago River green is full of spirit too! Back in 1961, Stephen Bailey, who was the business manager of the Chicago Journeymen Plumbers Local 130, spotted some bright-green marks on a plumber’s white overalls, and this, of all things, is what inspired the idea. Those stains were caused by a green plumber’s dye, which was used to detect leaks, and it was the first type of dye that was used to color the river in 1962.

While the mayor at the time had originally hoped to turn Lake Michigan a shamrock shade of green, the body of water proved too sizeable, so the plan was scaled down to the Chicago River. Over sixty years later, the dyeing of the Chicago River is a mainstay tradition in this city that’s predominantly of Irish descent.

Is the Chicago River Dye Harmful?

Now that the dye has switched to a vegetable-based, food-grade formula, it’s more eco-friendly. The Illinois Environmental Protection Agency (EPA) has even named the dye as “completely nontoxic,” which is good news for spectators, animals and the environment. The old dye was oil-based, meaning that it wasn’t so great for wildlife (picture those poor animals after oil spills!). The modern-day powder version is better for the little creatures who inhabit the waters of the Chicago River.

Next up, learn even more fascinating facts to add to your St. Patrick’s Day knowledge.