Web Exclusive: Warm Water Continues to Plague Northern Rockies Trout Fishing

This summer’s historic heat, growing wildfire threat, low precipitation and stream flows, and rising water temperatures are pushing local trout populations towards dangerous thresholds.

Warm Water Leads to Yellowstone Fishing Closures

There's little doubt that Yellowstone National Park and its remarkable native trout fishing serve as one of the cornerstones of the fly-angling world. And, in recent years, there's also little doubt that casting dry flies and bouncing nymphs in those famous currents has changed a bit as hot summer weather sends water temperatures to unsafe levels for trout.

With that in mind, beginning on July 15 this summer and continuing until conditions improve, certain rivers in Yellowstone NP were completely closed to fishing due to warm water temps and low river flows. Additional measures were implemented on July 26 as the warm water crisis for this summer season has continued to deepen.

Rivers and all of their tributaries having full closures for now—in part because of the recent hot weather and low stream flows, and in part because these streams are heavily influenced by geothermal features and don't cool off appreciably at night—include the Madison River, the Firehole River, and the Gibbon River downstream of Norris Campground.

Rivers and streams that close daily at 2 p.m. and remain off limits until sunrise the following day include the Lamar River (downstream of Cache Creek to its confluence with the Yellowstone River), the entirety of Soda Butte Creek, the entirety of Slough Creek, the Yellowstone River (from Tower Junction north to the park's boundary), the Gardner River (downstream of Osprey Falls north to the park's boundary), and the Snake River (from Forest Creek south to the park's boundary). 

Please note that these current closures of Yellowstone National Park rivers and tributaries could be joined by others as conditions warrant and include both the rivers themselves and their associated tributaries according to a National Park Service news release. 

Rivers not mentioned above will remain open to fishing according to park officials. Yellowstone Lake and other lakes within the famed park will also remain open to fishing from sunrise to sunset. 

Even for waters that remain open, Yellowstone fisheries experts indicate that water temperatures have already reached dangerous territory in many spots. With those water temps at or predicted to exceed 68 degrees Fahrenheit (20 degrees Celsius), and with stream flows on many rivers, streams and creeks at historic lows, these conditions are highly stressful to trout and potentially fatal. Yellowstone officials note that the closures in place will be reassessed when water temperatures cool down and water flows return to more typical summer conditions.

Widespread Montana Hoot Owl Closures in Effect

Yellowstone Park isn't the only famous trout water struggling with high water temps and low water flows. Numerous rivers in the Big Sky State are struggling as well, leading to a slew of Hoot Owl closures that prohibit fishing from 2 p.m. to midnight each day under the Montana Fish, Wildlife & Parks (FWP) mandates.

Rivers that had already seen portions of their waterway affected by hoot-owl regulations this summer include the:

• Big Hole River
• Beaverhead River
• Clark Fork River
• Madison Rover
• Ruby River
• Sun River
• Jefferson River (entirety)
• Silver Bow Creek (entirety)

Now joining those streams with hoot-owl closures put in place by FWP are the:

• Big Hole River (the entire river downstream of Saginaw Bridge on Skinner Meadows Road)
• Smith River (from Eden Bridge to the confluence of the North and South forks)
• East Gallatin River (the entire river)
• Gallatin River (from Amsterdam Road to the confluence with the Missouri River)
• Madison River (from Ennis Fishing Access Site (FAS) to Ennis Reservoir)
• Clark Fork  River (from Rock Creek near Clinton to the confluence with the Flathead River)
• Bitterroot River (the entire river, from the confluence of the East and West Forks to the Clark Fork River)
• Blackfoot River (from Cedar Meadow FAS to the confluence with the Clark Fork River)
• North Fork Flathead River (from confluence with the Middle Fork to the Canadian border)

Indeed just yesterday (August 1) it was announced that the lowest stretch of the Big Hole, from Tony Schoonen FAS (aka Notch Bottom) to its mouth on the Jefferson, will be under an all-day closure until further notice.

And according to Montana Free Press author Justin Franz, the recent addition of the North Fork of the Flathead River to those hoot owl restrictions is nothing short of historic. 

As Franz's story in the Montana Free Press notes, it's the first time that the FWP has ever put such restrictions on the Flathead in its northwestern corner of the Big Sky State.

“This is unprecedented for us up here,” said Dillon Tabish, regional communication and education program manager for FWP's Region 1.

Kenny Breidinger, fisheries biologist for FWP Region 1 that focuses on the west side of the Flathead drainage, said heat-induced stress of westslope cutthroat was the primary concern in the North Fork. 

Ironically enough, a year ago this week, FWP also considered instituting hoot owl restrictions on all three forks of the Flathead due to low streamflows at the time. That was avoided in 2023, but the hoot owl restrictions were necessary in late July 2024.

For such restrictions to be instituted, the FWP biologist noted that “…streamflow conditions must be deteriorating, fishing pressure (the number of people on the water) must be high and the temperature for a specific section of the river must hit a certain point for three days in a row.”

At the North Fork of the Flathead River, that temperature is 66 degrees and Breidinger said it has been above that for over a week at the time of the story’s publication, adding that decreasing streamflows finally convinced FWP.

Hoot owl restrictions stem from FWP's drought policy, which provides the agency with the ability to implement angling restrictions when river flows fall below critical levels for fish, when water quality is diminished, or when the daily water temperature exceeds 73 degrees for three consecutive days (unless otherwise noted, like on the North Fork of the Flathead). FWP also notes that water temperatures of 77 degrees or more can be lethal to trout.

FWP indicates that anglers might want to consider fishing areas with less stressful water temperatures and stream flow conditions like deep in larger lakes or reservoirs or higher elevation water bodies. To stay up to date, visit the FWP site here.

Western Trout Face Warm Water Dangers Elsewhere

As Fly Fisherman digital editor Josh Bergan noted this week, "...other Western states are experiencing the same high water temps but don’t have the ‘hoot owl’ rules in place so they just keep the fisheries open."

Idaho's Silver Creek—a world renowned spring creek—has been near or at 73 degrees several times already this summer according to Bergan. And Idaho’s Upper Salmon River has been over 70 degrees many consecutive days this summer.

These statistics prompted the Idaho Department of Fish and Game (IDFG) to re-release a statement on its policy, which is based on an IDFG study in eastern Idaho that concluded that, “...Idaho rivers during a hot summer showed catch-and-release angling did not harm the trout population.”

This unique finding goes against the common wisdom that doing so does harm trout populations, along with the policies of other Northern Rockies states.

“While mortality was higher at the hottest temperatures,” the article reads, “the number of trout caught was much lower because it was much harder to catch fish at those warmer temperatures. This phenomenon is well known to trout anglers, who often stop fishing in the heat of the day because catch rates are poor compared to cooler times of the day.”

Further south, rivers at higher elevations in Wyoming and Colorado seem to be in better shape but they are not out of the woods for the 2024 summer season if hot weather continues.

The Wyoming Department of Fish and Game did recently release an article that asks anglers to voluntarily “adjust fishing practices during the state’s hottest stretch of summer.”

“It’s that time of year when water temperatures are highest," said Alan Osterland, Game and Fish fish division chief. "Warmer surface temperatures have the potential to be lethal to trout. Warm water also holds less oxygen which can stress not only trout, but also all fish.”

Bottom line, if you're going to fish between now and the first chill of autumn and falling water temperatures, always bring your own stream thermometer to check the temps where you are fishing.

Orvis Post Notes New Research on Trout Safe Water Temps

Phil Monahan and the good folks at Orvis asked an important question recently, especially when considering the news items listed above. That question is simply this, "Are we wrong about current thinking on safe temperatures for trout fishing?"

The topic was covered extensively by Monahan in a recent Orvis post who noted that every year about this time, stories and graphics start circulating that warn trout anglers that as accepted convention goes, we should stop fishing for trout as water temps approach 70 degrees.

But perhaps that thinking is faulty as Monahan points to a new study from Keep Fish Wet that raises the idea that such thinking could be off a few degrees. He digs deep into a Keep Fish Wet article by Jamie Madden, who opines that the threshold of temperature related fish mortality is likely much lower than most current info graphics and state-agency press releases would suggest.

In distilling the scientific article—"Fishing for Trout in Warming Waters–Science-Based Angling Thresholds"—down to a single thought for summertime anglers to easily digest, it’s a thought that should raise some eyebrows and perhaps stimulate some changes in angling behavior. That statement from Madden reads: "The results of my literature review suggest the angling threshold of 68°F/20°C is too high for all the species I researched."

According to the Keep Fish Wet article: 

• “I found that the angling threshold is around 61°F /16°C for steelhead, rainbow, brook, and cutthroat trout. This number was determined from a combined 24 mortality studies and 9 sublethal impact studies and keeps temperature-based mortality under 5-10%.
• “Brown trout are known to withstand slightly warmer temperatures. With the data available (4 mortality studies and 1 sublethal effects study), I suggest an angling threshold of 66°F/ 19°C*.”

Importantly, as Monahan notes: “Be aware that this new literature review is not suggesting that we stop fishing a much lower temperatures, but it is arguing that we should all be more mindful.”

It's a worthy read, both Monahan's Orvis post and Madden's story, as we continue to battle the effects of hot weather, low stream flows, and lethal water temperatures this summer. Read more of the research here.

But Fishing Remains Good at Higher Elevations

All of this said, forecasted air temperatures in this so-called “Golden Triangle” of fly fishing are currently set to cool off for the foreseeable future, so there’s hope that we'll salvage a hopper season yet. In fact, the most recent report from Blue Ribbon Flies in West Yellowstone, Montana indicates that the changing of the calendar—September is now a month away—and some weather relief in recent days has delivered a few reasons for anglers in the cradle of Western fly fishing to smile just a bit right now.

"We've been the recipients of some much needed rain here lately and the fish have been loving it," wrote the iconic fly shop's Josh Almond in this week’s e-mail newsletter report. "While none of the restrictions have been lifted, our water is in much better shape than it was this time last week. Fishing has continued to be good throughout the area and there's always a good fishing option out there!"

The report notes that "The Madison is continuing to fish pretty darn consistently as we move into August", along with fair action in other spots including the Yellowstone, and at times as the weather allows, on Hebgen Lake too, although the Callibaetis hatch did sputter a bit in recent days with the rainfall. But Almond expects that hatch to pick back up shortly, something that fly anglers who thrill to stillwater hatches in the region will likely get excited about.

Almond also gives fly anglers visiting the region another option to consider as August fishing rolls onto the scene this week. With any luck, it will be worthy of a gold medal run at the end of a fly rod.

"Looking forward to next week our temperatures are climbing back up into the 80's," he indicated. "We expect fishing to stay strong through the morning hours and taper off a bit in the afternoons. 

"This means it's probably going to be a great time to enjoy one of the many small streams our area has to offer. Bucky and I both enjoy spending time on the little ‘cricks’ with either a 2- or a 3-weight and small selection of attractor dries. It's a great time leap frogging up a creek with a buddy or two and laughing about how lightning fast those little native trout can eat a fly!"

That—and some upcoming hatches—should get Montana fly anglers through the rest of this summer and have them rip-roaring to go as September’s autumn weather and superb fly fishing arrive in a few weeks. And that, of course, can be heaven on earth in the Yellowstone National Park region, if you like to fly fish for big autumn trout, that is.

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Lynn Burkhead is a Senior Digital Editor with Outdoor Sportsman Group.

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