No holiday or public festivity is likely more associated with one color than St. Patrick’s Day. Green hats, green shamrocks, and green beer. And green water. Since 1962, Chicago has dyed the Chicago River green in honor of the Emerald Isle. How did this come about? And is this tradition really “green” – in the sustainability sense of the word?
Green dye was originally put in the Chicago River as a contaminant tracker. The St. Patrick’s Day spectacle was born, so the story goes, when a member of the Chicago Plumbers Union Local 130 UA encountered a worker whose white overalls were covered in green stains from the tracer dye. Perhaps inspired by the unsuccessful 1961 attempt in Savannah, Georgia to dye its river green, the Chicago union group dumped 100 pounds of the dye into the river for the 1962 St. Patrick’s Day, “and the river kept its green look for a week.” Chicago’s Mayor Daley originally wished to dye Lake Michigan green, rather than the river; but he was talked out of the idea. 
The exact formula, ratio, and chemical used in the dye has changed many times. The dye used in the 1960s was disodium salt, an oil-based fluorescein that environmentalists argued would harm the river severely, despite its previous use as a tracking agent for preventing further pollution and sewage leaks.
The fluorescein dye was certifiably harmful to the environment, as recent tests on snail and mollusk populations in the Bliss Rapids region of Idaho demonstrate: they were exposed to tracer levels of fluorescein dye for 24 hour periods, and then tested for accumulation and detrimental effects. The conclusion was that 377 mg L-1 is the median lethal concentration for the Ashy Pebble snail, indicating a present, albeit low, risk to the mollusk populations resulting from just nearby groundwater testing and dye tracing applications. 
Fortunately, the use of this fluorescein dye was discontinued in 1966, when mounting concerns forced the responsible committee to find an alternative dye option that would cause less controversy. But what about the dye that is currently used? Does it stand up to in-depth scrutiny? Shouldn’t the public have a right to know what it is made of?
I began investigating these questions for a research paper in Dr. Daniel Macfarlane’s senior environmental studies seminar at Western Michigan University. Here’s what we do know. The current dye is a vegetable-based powdered dye, orange in color until it is mixed into the water. It is a forty to sixty pound mixture that keeps the river green for about five to six hours. It has to be approved by the Environmental Protection Agency and fulfill NSF standard 60 requirements, allowing it to be added to potable drinking water without negative effects to human or biome. While the move to a vegetable-based dye is undoubtedly a good thing for the ecosystem of the Chicago River, it forces us to ask if the addition of any chemical to a river simply for celebration is something we want to promote as environmental stewards?
Chicago is reluctant to reveal the exact dye they use, saying their celebration would cease to “be on television anymore” because other towns would do the same thing. However, many other communities (see below) are already dying their rivers too, so this excuse goes out the window.
Numerous entities and agencies have appealed for the release of the type and chemical composition of the dye, without any success. I did the same as part of a research paper I wrote in my senior capstone course in the Institute of the Environment and Sustainability at Western Michigan University. On November 1, 2016, I filed a FOIA request with the EPA, inquiring about the nature and safety of the dye being used in the Chicago celebration. Their response is as follows, excerpted from the letter I received:
“We have no information responsive to your request; however, EPA Region 5 contacted [REDACTED] in the Water Quality Standards Unit at Illinois EPA. He said an aquatic toxicologist at Illinois EPA, who has since retired, researched this issue about 10-12 years ago. The dye used is a food grade dye also used in medicine, as the colorant for antifreeze and as a tracer dye. Illinois EPA found that at the concentration used in the Chicago River, it is completely non-toxic. … We didn’t do a lab test on a sample of the dye [intended for the Chicago River]. EPA contacted the Plumbers Unions on what was in the dye. Then, EPA’s toxicologist reviewed the dye’s ingredient and deemed it safe.”
The EPA response was one of underwhelming assurance and ultimately it failed to answer my question. Granted, the EPA has approved the dye; yet, if it is truly harmless, Chicago should have nothing to hide.
In terms of chemical profiling, the EPA response allows us to speculate about what concentration of the chemical would be toxic, and the point at which each species in the ecosystem would reach the LD50: the lethal dose at which 50% of the population dies or experiences seriously detrimental health effects that can affect future breeding potential, cause malformed growth patterns, and reduce a species’ overall viability in an ecosystem.
There is an indirect method of testing the green dye used in Chicago. The city of Tampa, Florida has a similar, albeit newer, tradition called the “Mayor’s River O’Green”: in this St. Patrick’s Day celebration the city dyes the Hillsborough River a bright “kelly green.” This began in 2012, following an apparent trend in the green river phenomenon across the nation, including cities like Indianapolis, Jamestown, New York, San Antonio, and Charlotte.
The interesting point-of-fact here is that Tampa does not keep the dye they use a secret. Their dye is made by Bright Dyes Inc., and when a spokeswoman from the City of Tampa was asked whether the dye used in Chicago was the same product, she replied “I’m sure it is.” 
Let’s assume that the Chicago dye is in fact made by Bright Dyes. In the company’s catalog this dye has Product ID 105001 and is described as follows: “Fluorescent Yellow/Green Powder provides strong visual at 120,000 gallons /1 ppm dye.” Bright Dyes claims that their dyes are the “only full line of water tracer dye products certified by the NSF Standard 60,” although they offer no ingredients besides “vegetable based.” Indicating that even Bright Dyes feels that independent verification of safety factors is necessary, their data sheet states: “As always, the suitability of these products for any specific application should be evaluated by a qualified hydrologist or other industry professional.” 
It stands to reason that, if Bright Dyes is the only company that manufactures a dye that meets the requisite standards, Chicago must be using this Bright Dyes – so why all the cloak-and-dagger? After all, other cities have clearly caught on.
Or, the more troubling alternative is that Chicago isn’t using Bright Dyes – which means they would be violating the federal Clean Water Act.
The rhetoric used by the city’s media arm justifies the dyeing tradition, if only for its own sake. The city parade website describes the “greening” of the river as a “modern miracle.”  Organizers say that the dye works so well in the Chicago River because “the river is much more controlled in its flow” than most other waterways. This trait of riverine consistency doesn’t stem from natural happenstance, however, but because the river is so constantly regulated and heavily modified: e.g., it was reversed in 1900, and has been subject to many other hydraulic engineering interventions.
Dyeing the river continues and perpetuates the notion that we can modify rivers to suit our tastes with no regard to the consequences. Thus, even if the dye itself isn’t ecologically harmful, the process of dying the river can sustain harmful ecological ideas. The Friends of the Chicago River, for example, feel that the dye allows people to believe the river isn’t “natural,” therefore justifying its treatment a a sewer. Dyeing the river can be interpreted as a surreptitious disenfranchisement of the river. This power dynamic is exercised by the City of Chicago as an effort to further legitimize its historic manipulation of the river and to create a false narrative regarding the human relationships with the river.
The dyeing of the Chicago River will not end any time soon: the tradition has too much momentum and has become institutionalized. But we are progressing down a slippery slope of environmental manipulation, forgetting at our own peril that “Mother Nature always bats last, and she always bats 1.000.” 
 Moser, Whet. “Dyeing the Chicago River Green: Its Origins in the Actual Greening of the River.” Chicago Magazine.
 Stockton, Kelly & Moffitt, Christine. “Acute Toxicity of Sodium Fluorescein to Ashy Pebblesnails Fluminicola fuscus,.”
 Klein, Karen. “Is It Safe to Dye Rivers Green?” SafeBee. 14 March 2016.
 Bright Dyes. Technical Data Bulletin # 105001.
 Quote from Rob Watson: http://www.nytimes.com/2010/07/25/opinion/25friedman.html
Latest posts by Isaac Green (see all)
- Dyeing to be Green: The Chicago River and St. Patrick’s Day - March 17, 2017
Superb assessment. Alas, the American right wing looks at such things and says, “See? They always try to act so smart and ruin a good thing by saying we’re ‘killing Mother Earth.’ Never mind that it’s been going on for 50 years. Next, they’ll tell us we can’t use soda straws anymore. Oh, wait, they already are.”
Well, we must keep trying, regardless. Issues of shared concern, like the environmental impact of silly, pointless desecration of a natural resource to amuse the masses for a few hours, often are complex and they often do need intelligent consideration. Much more so the long-term implications from a social evolutionary point of view. Ah, but there I go, using my big words and trying to confuse the simple folk. But, if setting good policy were easy, anyone could do it, even the American right wing. But it’s not easy, so someone else will have do it.
Thanks for helping us with that.
According to some online shops* the product is simply fluorescein disodium salt. In addition, the physical data in the data sheet from the company Bright Dyes is in accordance with fluorescein disodium salt (e.g. the pH 8.5). So what Chicago and Tampa use to colour their rivers green is most probably the “good” old fluorescein disodium salt!
“Dyeing the river can be interpreted as a surreptitious disenfranchisement of the river.”
What gobbledygook. “Surreptitious disenfranchisement”???
How do you “disenfranchise” a river?
Hello Thomas, the concept of nature personhood and disenfranchisement is a relatively new development, both culturally and legally. Informed by Indigenous thought, various countries around the world are beginning to give rivers and other natural entities legal personhood, which Isaac Green is likely drawing on here. Here in Canada, in 2021, the Muteshekau Shipu (Magpie River) in Québec was the first river in Canada to be granted personhood. This is is a great article from The Narwhal on the topic: https://thenarwhal.ca/opinion-muteshekau-shipu-magpie-river-personhood/. If you read French, we’ve also got an article on our site by Caroline Desbiens: https://niche-canada.org/2021/05/07/personnalite-juridique-de-la-riviere-magpie-muteshekau-shipu-une-premiere-au-canada/. This is just a starting point for learning about this movement to provide rights to nature, and to, thus, recognize their disenfranchisement.