It's one of Chicago's most iconic -- and colorful -- traditions, and it's just around the corner.
Saturday, March 16, the Chicago River will magically turn a bright shade of green in honor of St. Patrick's Day. The tradition, put on by the Chicago Plumbers Union and dates back nearly 70 years, will coincide with Chicago's St. Patrick's Day Parade. The popular South Side Irish Parade is set to take place on Sunday, March 17.
But it doesn't last long. According to Choose Chicago, the color lasts only for "a few hours," so you won't want to miss it.
Here's the timing of the river dyeing, how to watch it live and more.
What time is the Chicago River Dyed Green?
The Chicago River is set to be dyed green Saturday, March 16 at 10 a.m., according to Chicago Journeymen Plumbers Local 130. The Chicago St. Patrick's Day parade is set to follow, beginning at 12:15 p.m. Typically, the route moves along Columbus Drive from Balbo to Monroe Street, allowing access to numerous downtown attractions before and after the parade.
Officials are reminding the public that the lower level of the riverwalk will be closed on March 16, with no access available via public stairwells in the area. Instead, revelers are asked to watch the festivities on Upper Wacker Drive, with the best views available between Columbus and Fairbanks.
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How is the Chicago River dyed green?
The Chicago Plumbers Union, Chicago Journeymen Plumbers Local 130, has been dyeing the Chicago River green in honor of the city's St. Patrick's Day celebrations for decades, with this year set to mark the 69th.
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For those who have never seen the process in person, each year the Chicago Plumbers union embarks on boats that putter along the Chicago River, with a rather curious concoction that sprays dye out of plumping pipes and spout pumps.
But the mysterious mixture doesn't come out green.
"If you were watching this for the first time you would think this is a mistake or a bad joke," the union said. "You see the dye is orange, and its initial color on the surface of the river is orange, and you would think to yourself what 'heathen would do something like this.'"
However, once the dye sets in, the color "in a stroke of luck" turns, and the "true color magically appears," the union said.
WATCH: Behind the Scenes: Creating Chicago's Iconic Green River Dye
According to Local 130, other cities have attempted similar feats, but never found success.
"We believe that's where the Leprechaun comes in," Local 130 says.
"As the late Stephen Bailey has said, the road from Chicago to Ireland is marked in green," the post regales. "From the Chicago River to the Illinois River, then to the Mississippi, up the Gulf Stream and across the Atlantic you can see the beautiful green enter the Irish Sea, clearly marking the way from Chicago to Ireland."
What's in the dye?
The actual recipe has never quite been revealed, the plumbers' union won't reveal its secrets.
The plumbers union, Choose Chicago says, "still holds the river-dyeing honors today." But you won't be able to find their recipe anywhere.
There is one thing the city does say about the dye, however.
"Their environmentally friendly dye formula remains a closely kept secret," Choose Chicago says.
How long does it stay green for?
Not long.
According to Choose Chicago, the green color lasts only for "a few hours."
How to watch the Chicago River dyeing live
NBC Chicago will stream the event live online, in our app and on the NBC Chicago streaming channel.
Why is the Chicago River dyed green and when did it start?
The story goes, in 1961, a man by the name of Stephen Bailey -- the business manager of the plumbers union -- was approached by "one of his plumbers who was wearing some white coveralls," a post by Local 130 says. It was then the union says, that Bailey noticed the overalls had been stained or dyed with "a perfect shade of green," or "an Irish green to better describe it."
When wondering how the coveralls could have turned such a tint, the tale continues, Bailey and his plumbers discovered that it was from to the dye used to detect leaks in the river.
"That's when Mr. Bailey bellowed," the Union declares, "Call the mayor ... we will dye the Chicago River green!"
And there you have it.
