The annual tradition of dyeing the Chicago River green for St. Patrick’s Day, which began in 1962, often raises questions about its environmental impact. Many wonder if this festive display harms the river’s ecosystem or poses risks to human health.
The Dye’s Composition
The substance currently used to color the Chicago River is a vegetable-based, non-toxic, and biodegradable powdered dye. While the exact formula is a closely guarded secret, it is widely believed to be fluorescein or a chemically similar compound. This orange powder turns green upon contact with water and is considered food-grade. This differs significantly from the oil-based dye initially used in the early 1960s, which raised environmental concerns and was discontinued in 1966.
Impact on Aquatic Ecosystems
Research indicates the modern dye has no significant adverse effects on the Chicago River’s aquatic life. A study by Austin Happel, a research biologist at the Shedd Aquarium, tracked tagged fish during the dyeing process. His findings showed no unusual fish behavior or reported fish kills. The Illinois Environmental Protection Agency (IEPA) states the dye is non-toxic at the concentrations used.
The Chicago River system has seen significant improvements in its ecological health, now supporting approximately 80 species of fish, a substantial increase from fewer than 10 in the 1970s. The dye dilutes quickly in the large volume of river water. While environmental advocacy groups like Friends of the Chicago River acknowledge the dye’s safety, they sometimes express reservations about the symbolic message the tradition sends regarding stewardship of the revitalized waterway.
Human and Environmental Safety
Concerns about human contact or water supply contamination are addressed by the dye’s properties and city infrastructure. The vegetable-based dye is considered harmless upon incidental skin contact. Chicago’s drinking water is sourced from Lake Michigan, not the river. The Chicago River’s flow was reversed over a century ago to divert water away from the lake, preventing sewage from entering the city’s primary water source. This engineering feat ensures the river’s contents do not affect drinking water.
The dye’s transient nature contributes to its low environmental impact. It typically maintains its green hue for about 5 to 6 hours, though traces may remain visible for up to two days. The dye does not accumulate in river sediment as it rapidly dissipates and breaks down naturally.
Regulatory Oversight and Dissipation
The dye’s application is subject to review by the environmental authorities. The Illinois Environmental Protection Agency (IEPA) has evaluated its safety data and concluded it has no toxic effect when used in the Chicago River. Although a specific permit for the dyeing event has not been issued, the IEPA’s assessment indicates compliance with environmental standards. Some environmental organizations advocate for a formal permit process under the Clean Water Act, citing reports of increased dye quantities and prolonged discoloration.
The dye’s presence in the river is temporary due to natural processes. Sunlight and water currents contribute to its dispersal and breakdown. The dye’s formulation is biodegradable, ensuring it does not persist in the aquatic environment. This natural dissipation prevents any long-term ecological alterations.