TroutCast Delivers Drought Forecasts for Montana’s Blue-Ribbon Rivers

For anglers, blue-ribbon trout streams are characterized by free-flowing water that’s clear, cold and full of fish.

But in the past decade, the chilly streams that sustain Montana’s prized trout species have been warming up and drying out as a result of rising global temperatures. As stream gauges across the state register historic high temperatures and record-low flows during summer months — a result of scant snowpack and an early spring runoff — fisheries managers are implementing fishing restrictions at an unprecedented rate, with potentially devastating ecological and economic consequences.

To help reverse the trend of needing to shut down a cherished Montana pastime on rivers and streams, and to promote proactive decision-making for fisheries management, drought response, and recreational angling opportunities, scientists from a multitude of agencies have collaborated on a new interactive web-based forecasting tool called TroutCast.

Launched this week, TroutCast is designed as an early-warning indicator to help forecast drought impacts on trout populations and support fisheries and water management across Montana’s renowned blue-ribbon rivers and trout streams.

Developed through a partnership among the U.S. Geological Survey (USGS), Montana State University, the National Oceanic and Atmospheric Administration National Integrated Drought Information System (NOAA-NIDIS), and Montana Fish, Wildlife and Parks (FWP), TroutCast provides seasonal and long-term forecasts to inform proactive decision-making for fisheries management, drought response, and recreational angling opportunities.

For the first time, the team has quantified how specific streamflow levels translate into trout production and trout abundance in Montana’s iconic rivers. TroutCast uses these relationships to support water planning and management by linking hydrologic conditions directly to ecological outcomes.

“TroutCast brings together decades of fisheries monitoring and streamflow records into a practical tool that managers and the public can use in real time,” Timothy Cline, assistant professor of ecology at Montana State University, said. “It reflects a growing scientific understanding that river flow is a primary driver of trout production in rivers, with abundance increasing during wetter periods and declining during droughts.”

By integrating long-term trout population monitoring data from FWP, USGS streamflow records, and weather information, TroutCast can generate seasonal (1–3 month) and long-term (1–3 year) forecasts of trout population trends and drought risk. The tool also estimates the likelihood of fisheries management actions triggered by drought-related low streamflows or elevated water temperatures.

“Cold-water fisheries across the West are increasingly vulnerable to drought, putting both trout populations and angling opportunities at greater risk,” Clint Muhlfeld of the USGS Northern Rocky Mountain Science Center, said. “TroutCast links streamflow and temperature conditions with trout population responses, enabling proactive, science-based decision-making that supports sustainable fisheries, recreational opportunities, and the long-term resilience of freshwater resources in the face of drought and changing river flows.”

“It brings together all the fish population and streamflow data from across the state into one portal,” Muhlfeld added.

For nearly two decades, Muhlfeld has been studying how increasing drought frequency and severity across the West have placed growing stress on cold-water fisheries by reducing streamflows, elevating water temperatures, and contributing to trout population declines.

And while stream flow is the master variable in assessing the quality of native trout habitat because summer flow declines reduce the amount of available stream habitat, record-high stream temperatures is an increasing concern to biologists.

“We all know trout need water, but for the first time we quantified how much water they need to sustain these fisheries and potentially grow them,” Muhlfeld said. “But what allowed us to do in terms of forecasting is examine whether there is a strong correlation between streamflow recruitment. So, if we have a good water year and streamflows are abundant, we can expect that, one or two or three years out, we will see the trout population grow. We figured this would be a great way to forecast the health of trout populations into the future.”

The changes scientists are forecasting into the future, both of trout population and streamflows, have important ecological consequences, Muhlfeld said. But they also have serious economic implications for communities that rely on recreational fishing, outfitting, and tourism, from the Flathead Valley to the Big Hole and beyond.

Indeed, in the 35 years since the late Robert Redford brought us “A River Runs Through It,” Montana’s fly-fishing tourism industry has grown by magnitudes. After spiking by 60% in 1992, the year the movie was released, the Treasure State’s seemingly indefatigable pastime has endured a 280% increase in nonresident fishing pressure while also surviving drought, reduced streamflows and warming water temperatures. And while studies have predicted that future climate change may cost Montana $192 million per year in revenue by 2080, a 2025 report from the University of Montana’s Bureau of Business and Economic Research (BBER), in partnership with FWP, revealed that angling is still a boon to the state’s economy.

Beyond fisheries conservation, TroutCast is expected to benefit local and regional economies by helping sustain recreational fishing opportunities and improving predictability around drought-related management decisions. USGS research indicates that anglers are already adapting to drought conditions by shifting fishing locations within Montana, Muhlfeld said, helping sustain economic activity even as long-term pressures are expected to increase demand for proactive decision-making support tools like TroutCast.

“This tool revolutionizes the state’s ability to communicate trends in fish populations, manage angling opportunities, and inform instream flows,” David Schmetterling, fisheries research coordinator for FWP, said. “TroutCast predictions allow us to be proactive by providing information for anglers, outfitters, and fishery managers to make decisions by better understanding how drought and streamflow affect these socially and economically important fisheries.”

The initial rollout focuses on Montana’s rivers, with planned expansion to the upper Snake River basin in Idaho and Wyoming, followed by broader application across additional drought-affected western states.

TroutCast was developed through a multi-agency effort initiated in 2022 and supports Montana’s Drought Management Plan, the USGS Integrated Drought Science Strategy, and the NOAA-NIDIS by improving drought early warning and providing actionable scientific information for natural resource management.

Water temperature strongly regulates the distribution, abundance and physiology of stream-dwelling fish. This is particularly true for cold-water species like bull trout and westslope cutthroat, although TroutCast’s initial rollout captures data only for nonnative rainbow and brown trout, which represent an outsized share of the trout species targeted by recreational anglers.

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