The Grand Canyon has a water problem
On July 4, 2025, around 5 o’clock in the afternoon, just as Americans were gearing up for a night of hot dogs and fireworks, a lightning strike on the North Rim of Grand Canyon National Park caused a spark that would soon grow into flames. For three months, hotshots battled the Dragon Bravo Fire—named for a nearby rock formation—under extremely difficult circumstances. High winds on July 11 whipped the blaze across several hundred acres, igniting lodges, a sewage treatment facility, and other crucial infrastructure in the national park. By the time the last embers were extinguished in late September, 145,504 acres were burned, and Grand Canyon officials were left to clean up one of the worst natural disasters in the park’s history, Re:Public reports.
Among the casualties were historic buildings and employee housing on the North Rim, including the iconic Grand Canyon Lodge. In the fire’s aftermath, extensive burn scars left large portions of the landscape vulnerable to rockfall, debris flows, and flash flooding during monsoon storms. Portions of the North Kaibab Trail, the main trail that winds more than 14 miles from the North Rim down to the Colorado River, grew more treacherous as burned trees turned into widow-makers and fire-weakened slopes destabilized. Much of the North Rim, the park announced in January, would remain closed until at least May 15.
But one of the most consequential impacts of the Dragon Bravo Fire was its effect on the park’s water. Nearly all potable water for the South Rim and Inner Canyon corridor has historically come from Roaring Springs, a cave-fed spring system on the North Rim supplied by snowmelt and rain on the Kaibab Plateau and delivered through the 12.5-mile Transcanyon Waterline. That system, says the park, provides the drinking water for more than 5 million visitors a year, plus about 2,500 resident park employees.
As the fire pushed into developed areas, it damaged and disrupted critical North Rim water infrastructure, including treatment facilities and essential pipelines. Ash, sediment, and fire-related contaminants were washed into springs and creeks. In the months since, scientists and park officials have been left grappling with deeper uncertainties: how fire retardant, burned debris, and post-fire runoff may affect groundwater, springs, and downstream water quality; how vulnerable the park’s aging water systems now are to future fires and floods; and whether reliable water delivery, already one of the Grand Canyon’s most fragile pieces of infrastructure, can be guaranteed in a hotter, more fire-prone future.
With the Grand Canyon on the brink of peak visitation, those unanswered questions now carry a new urgency for the season about to begin.
Few people know Grand Canyon’s water systems better than Mark Nebel, who served for 15 years as the park’s chief hydrologist before taking a buyout and retiring in April 2025.
“There are several things that make this all so concerning,” Nebel says. “And it all starts with the fact that the Grand Canyon is a karst system, which makes it extremely vulnerable to contaminants.”
A karst system is an underground drainage network formed when slightly acidic water dissolves soluble rock—in this case, mostly limestone. This process creates caves, sinkholes, underground rivers, and springs, with water moving rapidly and unpredictably through fractures rather than filtering slowly through soil. “We’ve documented in recent years that rainfalls on the North Rim show up in Roaring Springs within a matter of days,” says Nebel.
That means that contaminants on the surface, such as the fire retardant used to suppress the Dragon Bravo fire, are quickly flushed into the drinking water sources during rainstorms. For years, those retardants, mainly made by a Missouri-based company called Phos-Chek, contained heavy metals like chromium and cadmium (most likely byproducts of ammonium phosphate, a main ingredient in the retardant). Chronic exposure to these metals has been linked to cancer as well as kidney and liver disease. A 2024 study done by researchers at the University of Southern California’s Viterbi School of Engineering found that Phos-Check LC95 contained heavy metals four to 2,880 times greater than drinking water regulatory limits.
Since that study was published, fire crews everywhere have begun using another Phos-Chek retardant, MVP, which the company says is much cleaner. “We were able to get a sample and test the MVP product,” says USC associate professor Daniel McCurry, whose lab conducted the LC95 study. “We found that the concentrations of the heavy metals in Phos-Chek MVP were 10 to 1,000 times lower than LC95. So, if it did contaminate the water, it’s probably right around the drinking water threshold. It’s still probably worth getting it tested.”
According to Joëlle Baird, public affairs officer and communications lead for Grand Canyon National Park, initial tests showed no fire-retardant contamination. “To date, no contaminants have been detected in any of the analyzed samples,” Baird wrote in an email to Re:Public. “Several of these samples—collected in October, November, and January—were intentionally timed to coincide with groundwater ‘pulse’ events caused by rain and snowmelt on the North Rim. These pulses represent conditions most likely to transport surface contaminants into the groundwater system. The absence of detections during these events indicates that fire-related contaminants have not entered the park’s drinking water source.”
What’s most concerning, as it relates to fire retardant, is the ammonium phosphate itself, which is commonly used as a fertilizer and can cause toxic blooms of algae and bacteria when introduced to water. In several western rivers over the past two decades, large numbers of fish in streams and rivers have died due to algae blooms caused by high levels of ammonium phosphate.
Previous research had suggested that ammonium phosphate washes away and dissipates. But in June 2025, a study in Environmental Science & Technology, conducted using water samples from Racehorse Creek in southwestern Alberta, contradicted that thinking. Over the course of a year, phosphorus clung to sediment and travelled far downstream, actually becoming more concentrated as it went.
The new research shows the potential for future algae blooms, which could threaten endangered fish like the humpback chub, which spawns in Bright Angel Creek. Baird addressed that concern via email: “If monitoring were to indicate elevated nutrient levels or ecological impacts,” she wrote, “the park has the authority to implement operational adjustments, additional monitoring, or mitigation measures as needed to protect both drinking water and aquatic and riparian environments.”
In the aftermath of Dragon Bravo, the biggest issue muddying Grand Canyon’s water supply may be just that: turbidity, or how much sediment is polluting the water. “Turbidity has been an issue with the drinking water in the park for years,” Nebel says. “You can’t drink water that’s contaminated with a lot of sediment. The fire is going to add a lot more particles and ash to the water, and it’s going to make the springs much more turbid for longer periods of time.”
Testing for that is currently being conducted by Abe Springer, professor of hydrogeology and ecohydrogeology at Northern Arizona University. “Because of the karst system, snowmelt can get into the aquifers in days, not hundreds of years,” says Springer. “And fires cause soil erosion, which can both speed this up and cause more sediment to enter the aquifers.”
When turbidity does render the water undrinkable, the park is forced to shut off the water. This happened for a different reason last November and December, when a pipeline break forced the closure of all five South Rim lodges. To serve visitors and employees, the park then relies on 13,000 gallons of water stored in 11 tanks on the South Rim, which hold about two weeks of potable water under typical demand conditions. “The problem, even before the fire, was getting much worse,” says Nebel, “because now we see 100-year or 50-year rain events happening more often. What I don’t know is—and I asked for this information for many years—what is their plan if turbidity lasts a month or more?”
To that question, Baird says that water limitations would be imposed, beginning with limiting overnight hotel guests and escalating to a scenario in which the park closes and resident staff are evacuated. But the question of when that might be the case was not fully answered. “Evacuation decisions under the existing waterline system and current storage capacity are not tied to a single turbidity or tank-level threshold,” Baird wrote, “but are instead driven by water tank levels in combination with the need to prioritize fire suppression capability, maintain system pressure, and protect public health and safety when water treatment or delivery cannot be reliably sustained.”
Complicating matters is the park’s aging pipeline, which draws water from Roaring Springs. The Transcanyon Waterline was only expected to last for 30 years, and has now been used for at least 55. Since 2010, it’s broken more than 85 times, and each repair can cost more than $25,000. Pipeline breaks can force lodges to close, meaning visitors must vacate.
Beginning in 2027, a new $200 million pipeline will draw water directly from Bright Angel Creek to serve the South Rim (the Roaring Springs pipeline will still be used for the North Rim). But since the fire, turbidity has at times caused Bright Angel to run black with ash. “A few years ago, when we had a high snowfall year,” says Nebel, “we put in turbidity-measuring devices in Bright Angel Creek and the turbidity was high, to the point the water wasn’t potable, for more than a month. And that was before the fire.”
Just as concerning is a recent report by the Arizona Water Science Center which showed that water in Bright Angel Wash, an ephemeral drainage below the South Rim’s wastewater treatment plant, is tainted with small amounts of pharmaceutical drugs, including an antihistamine, an anticonvulsant, and an antidepressant, as well as polyfluoroalkyl substances (PFAS), often used to waterproof outdoor gear and nonstick cookware. PFAS are linked to cancer and infertility.
Meanwhile, a new water treatment facility is under construction at the bottom of the canyon, set to go online in October 2026. It won’t filter out PFAS or pharmaceutical compounds, but according to Baird, water samples look good so far. “An ongoing joint study between the U.S. Geological Survey and the National Park Service has sampled water at the new intake and throughout the upstream watershed,” she wrote, “and PFAS, pharmaceuticals, and other contaminants of emerging concern have not been detected in this drinking water source to date.”
Nebel is not convinced that the new filtration system can keep up with current rates of turbidity. “While the system was designed with an understanding that turbidity events may increase following wildfire, it is not intended to treat extreme post-fire debris flows directly,” says Baird. “To account for this, the future intake system is designed to automatically shut off and rely on storage when turbidity thresholds are met.”
Mark Nebel believes that the new system will be put to the test almost immediately after it is complete, in the early summer of 2027, when monsoons blow through the park and wash thousands of gallons of rainwater through the karst system and into the drinking water.
This spring and summer, though, during the first big runoff period since the fire, the park will need to rely on the current water infrastructure. Which means it may see multiple closures.
“Turbidity will be higher, and high turbidity events will occur more often and will be longer than they would have before the fire,” says Nebel. “That I can say for certain. [The new system] could run splendidly for a couple years until they get a high snowfall event. But we were never satisfied that the design had addressed that turbidity question. And it’s only gotten worse with the fire.”
This story was produced by Re:Public and reviewed and distributed by Stacker.
