Every summer, trout streams in the West face hot, low water conditions, making for tough fishing—and sometimes lethal conditions for trout. In Montana, famed trout streams like the Big Hole and Beaverhead are plagued with fishing restrictions and sometimes full-on closures in July and August. But what if there was a way to nip the problem in the bud and increase the overall water supply to begin with?
Researchers are exploring exactly that with a method called “cloud seeding.” The practice involves injecting a chemical compound, silver iodide, into the atmosphere during winter months, where it encourages the formation of ice crystals in clouds and subsequently increases snowfall. A deeper snowpack can then extend runoff later into the summer, keeping trout streams cooler and more productive.
Several states, like Utah, Idaho, and Nevada, have been experimenting with the technique for over a decade, and all three report increases in snowfall of 4% to 13% in test areas. Idaho claims to produce 1.24 million acre-feet of water via cloud-seeding annually, with target drainages including the Snake and Payette rivers. Now, Montana is exploring the use of similar tactics to improve conditions in the Big Hole drainage, which in recent years has seen major fish die-offs.
Historically, there were about 900 brown trout per mile in the Big Hole River, but within the last five years, that number has dropped to around 300, according to local fisheries biologist Jim Olsen. The exact cause of the decline isn’t entirely known, but biologists’ best theory is that low flows cause shallow back-marshes to dry out, leaving juvenile fish to perish in the main river channel with no shelter from predators.
While water conservation groups have made their best efforts to improve irrigation efficiency in the basin, there’s no legal basis—or desire—to claw back water rights from irrigators, so the state has turned to the root of the problem: water availability. That led the legislature to appropriate funds in 2023 to a cloud-seeding feasibility study in the mountains surrounding the Big Hole. The results were just released this summer, and they appear to be promising.
The study—which was completely theoretical, but based on actual data about local atmospheric conditions, weather patterns, and snowpack—used mathematical models on a supercomputer to test different scenarios for injecting silver iodide into the atmosphere. About half of the scenarios simulated dispersing the chemical into the air from towers installed on the ground, and the other half explored using airplanes to distribute the silver iodide above the Beaverhead, Anaconda, and Pioneer mountains.
According to the models, only about 12 to 24 days over the course of a winter (November through February) would provide favorable conditions for cloud-seeding, but those handful of days could have big potential. Under certain scenarios, precipitation—measured as the total water content in the snow—could increase by up to 1/16 of an inch during a single storm in localized areas. That might not seem like much, but over multiple storms and across the entire basin—which averages only 14 inches of precipitation a year—it’s a significant increase. Cumulatively, it could total 20,000 to 60,000 acre-feet of water per year. (For reference: 40,000 acre-feet would be enough to serve about 80,000 homes for a year, or irrigate 10,000 acres of alfalfa for a single season.)
In terms of cost, the Montana study estimates that cloud seeding would run taxpayers $10 to $60 per acre-foot, depending on whether “ground seeding” or “aerial seeding” is used. Idaho has managed to decrease its cost-per-acre-foot to about $3.50. Regardless of the price tag, it will be up to the Montana state legislature to sign the check and actually implement a pilot project.
Then, there’s also the issue of convincing citizens that cloud-seeding is safe. Idaho has clearly struggled with the issue, as witnessed by a state web page debunking the differences between airplane contrails and cloud seeding.
Even if a project does come to fruition, it’s not an end-all, be-all for the Big Hole. “It’s not going to cure all our ills,” Michael Downey, a program coordinator with the Montana Department of Natural Resources and Conservation, told a local news outlet. “It’s one more tool in the toolbox, and so if we can have a little bit more moisture for irrigation, and for fish, and for everybody else come the next season, then that’s worth looking into.”
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