A pink dye allowed researchers to trace an invisible journey beneath Florida. After injecting it into a sinkhole at Lake Jackson, they detected it 35 days later at Wakulla Spring, about 30 kilometers away. The finding provided evidence of an underground connection between the two sites.
The experiment took place in September 2017 and was published in December 2024. Its interest goes beyond geological curiosity, because it helps to understand how substances can move through an aquifer that supplies drinking water. However, only a small portion of the dye reached Wakulla.
How They Tracked the Trail
Researchers Seán E. McGlynn and Alan W. Niedoroda used rhodamine WT, a fluorescent marker detectable in very small amounts. On September 19, 2017, they injected it for 6.5 minutes into a sinkhole at the bottom of Lake Jackson, near Tallahassee.
The idea was straightforward. If the tracer appeared at the monitored springs, it would confirm that a portion of the water had travelled along the underground route. To detect it, the team combined sensors with carbon collectors that trapped the dye as it passed.
The main peaks appeared 35 days later at Wakulla and at the nearby Sally Ward Spring. The study records detections at five springs and estimates an average travel speed of about 800 meters per day. That figure reflects the conditions of the test, not a fixed rate for all groundwater.
A Network Within the Rock
How can water travel such distances unseen from the surface? The answer lies in karst terrain, where the dissolution of rocks such as limestone has created cracks, cavities, and conduits. Through those openings, a large part of the groundwater flows.
The United States Geological Survey explains that these aquifers operate in two ways. Fractures and conduits facilitate water movement, while the surrounding porous rock stores much of it. It is an uneven system, with zones that transmit water more readily than others.
In the case of Lake Jackson, detections at different springs point to a network that branches out and reconnects. The experiment allowed identifying connections between distant points, though it did not map every bend of the path. Knowing where the dye appeared does not equate to having a complete map of the subsurface.
The Dye That Didn’t Reach
The amount detected at Wakulla was small compared with what was introduced into the lake. The authors interpret that much of the dye dispersed through the limestone, although it could also have moved through conduits that were not monitored.
The work is exploratory in nature and does not allow a precise accounting of the dye, i.e., to determine where all the dye ended up. Therefore, the conclusion should stay within what was observed. Some of the lake water reached distant springs, but it was not demonstrated that all followed that path.
Why It Matters When You Turn on the Tap
The Florida Department of Environmental Protection notes that the Floridan Aquifer supplies drinking water to residents of Leon and Wakulla counties. It also feeds springs like Wakulla, so studying these connections has direct, nearby relevance. What happens underground matters at home as well.
In August 2021, the Florida Geological Survey announced another test in the Porter Hole sinkhole, which had become exposed as part of the lake dried up. That investigation used green fluorescein and aimed to verify a connection suggested by an earlier tracing. It was a different campaign from the 2017 pink-dye experiment.
The scale helps explain the interest of these studies. According to Florida State Parks, the area that supplies water to Wakulla covers roughly 2,525 square kilometers, spanning from northern Florida to southern Georgia. Protecting the spring thus requires looking far beyond its shoreline.
What Later Research Adds
The dye-tracing highlights pathways through which nutrients and contaminants could also move. That justifies monitoring water inputs into the aquifer, but the experiment by itself does not prove that drinking water is contaminated. It also does not allow attributing the same behavior to all substances.
A study by Kyle Compare and Ming Ye, published in November 2025, adds another nuance. By analyzing the lake drawdowns of 2021 and 2022, they found temporary chemical changes in a well about nine kilometers away, but did not observe those effects at Wakulla. This is an important distinction between detecting a tracer and measuring changes in water composition.
The work on the pink dye was published in the Journal of Cave and Karst Studies. The follow-up research on the chemical effects of the lake drawdowns has been published in Environmental Earth Sciences.
Image: Hannes Grobe / Wikimedia Commons (CC BY 3.0)
