Trout die off in Montana's Big Hole River

The last few years have been hard on Montana’s famous Big Hole River. So has the rest of the upper Missouri River Basin for that matter. Low snow packs plus early and dry summer head lead to historically low water levels in the rivers, while taking a serious toll on the trout population.

The Big Hole River runs through the sparsely populated Big Hole Valley in southwest Montana and into the Centennial Valley. 

The river is a freestone river, meaning no man made impediments block the flow of water from source to tributary, unlike the other rivers in the area like the Beaverhead and Ruby. The Big Hole is known worldwide as a blue ribbon trout fishery, a designation based on criteria which addresses water quality and quantity, water accessibility, natural reproduction capacity for fish, and angling pressure. 

This designation is in serious danger, however, as alarm bells are sounding in relation to the river’s once robust trout population.

During peak, quality, water years like 2011 through 2013, Big Hole fish biologists counted up to 2,000 brown and rainbow trout per mile in the river. As recently as 2023, however, biologists counted 500 fish per mile.

The loss of water volume has led to an increase of ambient water temperature, loss of available habitat and the proliferation of disease and fungus.

According to Trout Unlimited’s Conservation and Government Affairs Director Clayton Elliot, the diseases and funguses are nothing new affecting the fish.

“These aren't new pathogens, they are the same things that have affected fisheries for a long time, they are just more prevalent in these low water years,” Elliot said.

“You put a number of fish into a stressful situation and low real estate and you're going to get health issues.”

Trout are a cold water species, preferring a temperature range between 45 and 60 degrees. When water temps start rising above this range, their health declines and they become overly stressed. 

Elliot notes that in these stressful warm water situations something as small as a cu from a predator can easily lead to infection and death. 

“The problem is not disease, its water and habitat, and it’s nothing surprising being that the fish are living in difficult conditions,” Elliot said.

Elliot went on to reference fatal whirling disease which claimed prevalence in the 90s.

The disease involves a microscopic parasite that attacks a trout’s cartilage tissue on their head and spine, causing them to spin when fleeing a predator or trying to feed. According to Elliot, after state governments and agencies spent millions trying to combat the disease, the one true cure turned out to be cold and plentiful water.

Elliot did say there is one new ailment anglers and biologists are seeing where open lesions are found on a trout's head, looking like it met the business end of a cheese grater. He says that these”cheese grater heads”, as they are commonly called, are suffering from a secondary infection after acquiring an initial one known to science. 

The drought conditions aren’t just causing problems for the adult trout, however, but their offspring as well. 

Bad water also leads to poor spawning and recruitment. Fisheries biologists found that brown and rainbow trout are having a harder time reproducing in the warm water. This can be explained as simply as there not being enough spawning gravel underwater for fish to reproduce in. The eggs that do get laid and hatched also have a harder time getting from the gravel spawning grounds to becoming a two year old fish, however.

Elliot points to the trend of dryer winters and earlier runoffs and summer heat as a future challenge conservationists must face head on and they aren’t just for Montana.

“A lot of these drivers are a forbearing of future problems of the West,” he said.

“It’s coming to a head in the upper Missouri basin, (right now) but this is applicable to everywhere in the West. The supply of water is changing with climate change. We are getting less moisture in some places and different moisture in other places (rain instead of snow) and the timing of that flow (earlier runoff, higher peaks of runoff and more low flow events) is changing."

Some critics note that the Big Hole River has dried in the past and that dry winters and hot summers are nothing new. 

While it’s true the Big Hole has seen its fair share of dry weather, the extremes of these low streamflows are hitting new records.

The 80s and mid 90s saw droughts hit the Big Hole where water levels measured under 300 cubic feet per second for around 20 days at a popular fishing access site. 

In contrast the levels of the river in 2021 dropped under 300 cfs for around 96 days and 45 days under 200 cfs at the same access site.

 2022 saw 67 days under 300 and 24 days under 200

In both years the 300 cfs level stretched all the way into November, before raising back up, when previously it went into around September. This is especially detrimental considering brown trout typically spawn in late October.

While state and Federal officials don't have an answer to a changing climate, yet, Trout Unlimited has been instrumental in helping the state get funding to better understand the problems they are dealing with. 

Funding from the Dingle Johnson act, which funds fishing conservation from the sale of fishing licenses, was procured in help by Trout Unlimited. The funds are now going toward a four pronged study of the Big Hole watershed. The four prongs will tackle: Adult mortality, fish health, better understanding of recruitment and angler impacts.

Adult mortality and fish health (prongs one and two) 

Thousands of fish have been tagged and anglers are encouraged to report them when they catch one. This allows a better understanding of how disease and environmental factors are leading to pathogens, affecting the overall health and killing adult fish.

Better understand recruitment

How do fish go from egg to a two year old adult? This aims to get a better understanding of where these fish are coming from, specifically looking at creek tributaries. Ear bones in fish provide age rings that can be counted like in trees. Biologists can also match the chemistry in each ring of the ear bone to creeks where the fish were spawned and where they lived when they were one, two, and three-years-old. This effort can lead to a road map for the next 50 years of conservation efforts by giving biologists the knowledge of where to focus their conservation efforts. Stream habitat projects could be more directed toward important spawning creeks, instead of main river stems, for example. Knowing where the critical parts of a fish's life are lived can help better utilize and manage water throughout the season.

Angler impacts 

Catch and release vs harvest, how many times can a fish be caught before it dies, flies vs artificial lures, lures v live bait are all factors that will now be studied better than ever. Which, if any of these, impact fish the most? Biologists don't actually know the answers to a lot of these questions from a scientific standpoint. So hopefully a better understanding can help inform future regulations. If barbless hooks, for example, actually make a difference then those conversations need to be had.

The other component to future management of this historic fishery is water management. The Big Hole and Centennial Valleys are home to large agricultural farms and ranches. Those ranches all have historic water rights to the rivers for the use of irrigation. 

Most of these water use rights were established in the late 1800s and early 1900s, meaning the weather patterns today are drastically different. Historically these rights were meant so ranchers could irrigate their fields during high water runoff, which provided more water and typically happened in June. Now with high water runoffs happening more prominently in May, the June water usages are drawing from an already low river system.

According to Elliot, though, ranchers are good partners to fish and he doesn’t want to see their water uses drastically affected. A robust ag economy can help protect from rural sprawl, which can use far more water. In the BIg Hole, widespread flood irrigation is also critical for protecting late season water returns. When peak flows are distributed into the ground, it adds back to the ground water refilling aquifers and becomes part of the hydrologic cycle again.

The future may be uncertain for water, trout and anglers in the Upper Missouri watershed, but science and conservation partnerships are on the job to protect the special rivers anglers call home.

“We are in a tough situation, but we are doing a lot of really good work. We are working hand in hand with Montana Fish Wildlife and PArks which is leveraging tremendous resources for today and tomorrow,” Elliot said.

“The things we can learn will make a difference today and in the future, like they did with the Blackfoot River in the 90s. FWP (and Montana’s region three) have stepped up in a tremendous way."

As long as there are anglers who live for the flash of wild trout, snow capped peaks and wild winding rivers, there will always be hope.

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