CHICAGO — It’s been a time-honored tradition for almost 50 years: Dyeing the Chicago River green for the annual St. Patrick’s Day parade.

But how to they do it?

CBS sister station WXRT-FM (93.1) went behind the scenes with Mike Butler, who has led the coloring crew since the first dye job back in 1962.

Butler says they have perfected the process over the past 49 years and have never missed a year–no matter the weather.

But he prefers to keep the details a secret, although he wants to assure the public that the process is environmentally safe.

Listen to the interview with Butler from 2010.

Watch some video and check out some photos of the coloring in progress in 2010.

The coloring tradition continues on Saturday, starting at 10 a.m., just east of Michigan Avenue. The annual St Patrick’s Day parade steps off at noon. Click here for the parade route.

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