In 2020, Tim Lahey became the Butte district ranger, managing a portion of the 3.39 million-acre Beaverhead-Deerlodge National Forest. The two reservoirs tucked up in one of its mountain basins provide nearly 60% of Butte, Montana’s water supply, and Lahey knew his new job would not be easy: Those reservoirs were under threat, and had been for decades.
In the early 2000s, mountain pine beetles swarmed the basin, munching through and killing thousands of lodgepole pines. Nationwide, the insects have killed trees on nearly 8 million acres. Today, roughly half of the trees around the Basin Creek Reservoir are dead. Some are still standing, just waiting to fall; others are piled on the forest floor in a messy maze. If a fire started in the forested hills surrounding the Basin Creek Reservoir, it would likely burn hot and fast. It would not only be difficult and dangerous for firefighters to navigate the downed timber; the fire would also likely kill some of the remaining trees, destabilize the soil, and send sediment, pine needles and ash into the reservoirs and creek below. And that would be devastating for the city’s primary source of drinking water.
Lahey began meeting with Jim Keenan, then the chief operator of the water treatment plant downstream.That facility was designed to treat pristine alpine flow, not post-wildfire slurry. The 300-micron strainers it uses to clean out sediment have tiny holes the size of the “o” on a penny’s “In God We Trust.” “It wouldn’t take too much to clog it up,” Keenan said.
The reservoirs were under threat, and had been for decades.
Butte’s predicament is shared with towns and cities across the West where the water supply flows from fire-prone forests. Wildfires often force municipalities to rely on a patchwork of alternate water sources in the short term, and to spend more money over the long term to decontaminate their polluted sources. In 2014, for example, rains after a wildfire sent 300,000 tons of sludge into the Rubicon River, polluting drinking water in Auburn, California, that became twice as expensive to treat for several years. In 2020, wildfires dirtied all four watersheds that Greeley, Colorado, uses for its drinking water. The city had to pull water from its reservoirs instead of its usual river and make water swaps with agricultural users to meet demand. Cleaning up the affected watersheds is costing $30 million or more.
With wildfires becoming larger, more frequent and more widespread, more forests are burning — and that could affect many communities’ drinking water. According to the U.S. Geological Survey, 80% of the freshwater resources in the country originate on forested lands. Risk varies widely by location, but roughly 3,400 public drinking-water systems — including Butte’s — are located in watersheds within national forests. That’s why local, state and federal agencies are racing to thin thousands of acres in Butte’s watershed over the next few years.
Credit: Will Warasila/High Country News
BARBED WIRE and a sign stating “closed to public access due to wildfire risk” greeted us as our truck pulled up to the entrance of the Basin Creek Reservoir property in mid-July. A handful of fires start nearby every year, underlining the urgency of thinning the deadfall. “We’ve been fortunate to catch them so far,” Lahey said, at the wheel. Keenan, now the treatment plant’s superintendent, sat in the back as we wound around the rutted and bumpy roads up to the reservoir.
Both men have given tours of this area and its predicament several times, including one high-profile visit by Gov. Greg Gianforte, R, and Forest Service Chief Randy Moore in June 2023.“I think we’re already living on borrowed time,” Moore told Montana Public Radio. Six weeks later, the Beaverhead-Deerlodge forest supervisor and Lahey requested what’s called an “emergency situation determination” from agency leaders to jumpstart the removal of flammable vegetation. Moore approved, and the following week, a crew began cutting dead trees.
With wildfires becoming larger, more frequent and more widespread, more forests are burning — and that could affect many communities’ drinking water.
Executing a large-scale project like this requires collaboration. Silver Bow County, home to Butte, owns only a narrow strip of land encircling the reservoir, 975 feet at its widest. For buffers and fuel breaks to work, the Forest Service, which manages the rest of the land, needed to get involved, too. More than 450 acres of county and federal land will be thinned of flammable vegetation, with the piles neatly stacked and left to be burned this winter.
Removing some flammable vegetation isn’t a guarantee against fire; no such assurance is possible. Rather, managers believe that reduced vegetation will slow a flame front and reduce the height of the flames, improving firefighters’ chances of safely containing it. Whether this works is up for debate: Research from scientists at the University of Colorado, Boulder published in 2015 found that mountain pine beetle outbreaks don’t necessarily increase wildfire risk, despite leaving so many dead trees in their wake. Another study, published in 2011, found that pine beetle outbreaks may actually reduce, not increase, the potential for crown fires in the Greater Yellowstone ecosystem. But while a handful of comments received during the environmental assessment process questioned the value of thinning to lessen wildfire risk, the Forest Service says its modeling shows that the project will work, shortening flame lengths on the hot, dry summer days that cause the most concern.
RECOVERY FROM a wildfire’s impact on Butte’s drinking water could take a decade and cost over $30 million, Keenan estimates. That includes dealing with all the sandy sediment, no longer bound to the hillside by roots, that would need to be dredged out of the reservoir before it could return to full capacity. A study published in 2017 predicts wildfires’ increase in frequency and magnitude will more than double the amount of sediment that makes its way into one-third of the watersheds in the West, reducing how much water the reservoirs can hold.
Wildfires can pose other threats to water supplies far downstream of reservoirs. Testing has revealed carcinogens in drinking-water systems after urban fires in California, Colorado, Oregon and Maui. There are ways to proactively mitigate this, such as switching from plastic pipes, which can leach chemicals into the water, to metal ones, or installing backflow prevention devices to keep contaminated water out of the general water supply, and ultimately, homes and businesses. But these changes require planning from states, utilities and federal agencies. “We’re still in a very reactive phase,” said Andrew Whelton, an engineering professor at Purdue University who focuses on restoring safe drinking water post-fire.
Yet proactive work is already beginning at the source, in the tangled forest outside Butte. As we drove around the Basin Creek Reservoir in mid-July, the Montana sky was starting to fill with smoke from a rapidly growing wildfire to the north, outside Helena. The acrid haze served as a reminder of the threat of wildfire, never too far off throughout the summer and fall. “If we can buy ourselves a year or two, I’ll feel a lot better,” Keenan said. In the basin’s race against the clock, chainsaws would begin whirring the following week.
Note: This story was updated to clarify Tim Lahey’s role as the Butte district ranger in the Beaverhead-Deerlodge National Forest.
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This article appeared in the October 2024 print edition of the magazine with the headline “Consider the source.”
