Ahhh … St. Patrick’s Day in Chicago.

While for some the holiday may mean green beer and lots of partying, one thing’s for certain: Chicago’s estimated 200,000 residents of Irish heritage take their traditions seriously.

And there’s no more iconic Chicago St. Patrick’s Day tradition than dyeing the Chicago River green.

The history of the green river flows back to the local plumbers union. It’s been sponsoring the dye job for more than 60 years.

The story goes — as the plumbers tell it — that business manager Stephen Bailey got the idea from seeing a plumber in stained green coveralls.

See, the city was working to enforce restrictions on waste going into the river during construction projects. Plumbers were using dye to help trace the flow of wastewater and detect leaks.

Bailey and his pal, Mayor Richard J. Daley, initially considered dyeing Lake Michigan before ultimately picking a portion of the more manageably sized Chicago River.

And so, in 1962, the river got its first festive dye job.

Bailey waxed poetic, telling reporters the dye would connect the city to Ireland — flowing from the Chicago to the Illinois River, on to the Mississippi, up the Gulf Stream and across the Atlantic, into the Irish Sea.

The city has tried a few dye distribution methods over the years. Today a couple of motorboats do the job, turning a roughly quarter-mile stretch of the river downtown just the right shade, using what organizers say is an orange, vegetable-based powder that turns green on contact with the water.

The exact dye recipe has always been a closely guarded secret.

Some local environmental groups have pushed back against the tradition, like Friends of the Chicago River, who feel it harkens back to a bygone era when the river was treated as a quasi-sewer rather than a living body home to fish and wildlife.

But regardless of one’s stance — there’s no denying the tradition’s influence.

Other U.S. cities have taken the idea, dyeing their own rivers and canals each March.

And with thousands gathering along the Chicago River every year to see it all unfold, the tradition doesn’t seem ready to “dye” anytime soon.