Is the dye in the Chicago River really green?

On Saturday morning, an hour or so before Chicago's annual St. Patrick's Day parade, members of Chicago's Journeymen Plumbers Union added about 40 pounds of dye to the Chicago River, temporarily transforming a stretch of the waterway into a vivid green.

Ironically, the dye itself is orange. But once it mixes with the water, it becomes a bright emerald. "This spectacular transformation," notes the  parade committee's website, "ranks right up there with the parting of the sea by Moses and the Pyramids of Egypt."

(If you've ever wondered what the word "blarney" means, now you know.)

According to parade organizers, the tradition of dyeing the river dates to 1961, when Stephen Bailey, a business manager for the plumber's union, was visited by a plumber whose coveralls were stained green. The stains, it turned out, came from a special dye used to detect leaks. That year, the city had begun enforcing pollution controls, and the plumber was using the dye to locate the source of illegal waste disposal in the river.

But Mr. Bailey saw a different use for the dye. The following year, with the consent of city officials, the union dumped 100 pounds of a disodium salt called fluorescein into the river. It worked a little too well, turning the water was green for a week. Eventually they hit upon an amount that would turn the river green for just one day.

But fluorescein can be toxic, and environmentalists, concerned about the welfare of the river's goldfish, lobbied to have the dye replaced with something more eco-friendly. They succeeded in 1966, and the parade committee agreed to switch to what they say is a vegetable-based dye.

But the dye's exact ingredients are a closely guarded secret. The parade committee compares the formula to that of Coca-Cola. In a 2003 interview with the Columbia Chronicle, a student newspaper, a parade organizer compared revealing the dye's composition to "telling where the leprechaun hides its gold."

Even though they won't say what's in the dye, the parade committee insists that it's nontoxic, and claim that "the formula has been thoroughly tested by independent chemists and has been proven safe for the environment."

But environmental regulators in other cities have rejected plans to dye their rivers for the Irish holiday. In 2005, environmental regulators in Broward County, Fla. rejected plans to dye Fort Lauderdale's New River. And this year officials with Michigan's Department of Environmental Quality nixed plans for a dye job for the Saginaw River.

That said, 40 pounds of dye is a proverbial drop in the bucket compared to all the other stuff that's in the Chicago River. The Illinois Department of Public Health advises against dining too frequently on certain fish caught in the river because of concerns of mercury and polychlorinated biphenyls, a type of industrial chemical that the EPA has labeled a probable human carcinogen.

It seems that Bailey, who originated the idea of dyeing the river almost a half century ago, had a sense, albeit an exaggerated one, of ecological interconnectedness. A site sponsored by parade organizers quotes Bailey:

"The Chicago River will dye the Illinois, which will dye the Mississippi, which will dye the Gulf of Mexico, which will send green dye up the gulf stream across the North Atlantic into the Irish Sea, a sea of green surrounding the land will appear as a greeting to all Irishmen of the Emerald Isle from the men of Erin in Chicago land, USA."

Incidentally, what leprechauns hide their gold in is known as a crock.