Bull trout were so significant to the Salish and Pend d’Oreille people who originally inhabited the Missoula Valley that they called it “Place of the Small Bull Trout.”
The name specifically refers to the area near the confluence of Rattlesnake Creek and the Clark Fork River where bull trout once provided an abundant food source for the tribes. Today, bull trout are a threatened species due largely to rising temperatures and warming waters that make it difficult for the species to survive.
But the rehabilitation of mountain dams in the Rattlesnake Wilderness and National Recreation Area may help bull trout spawn by increasing streamflows and providing cold water during hot and dry summers. That option is one of many the city of Missoula is considering as it determines the future of the dams.
The Rattlesnake Wilderness is currently home to 10 dams built between the 1920s and 1930s that were historically used to augment Missoula’s drinking water, which came from Rattlesnake Creek. Following a giardia scare in 1983, the Mountain Water Company switched the city’s drinking supply to an underground aquifer, and the dams went mostly unused.
In 2017, the city of Missoula acquired the Mountain Water Company, and with it the responsibility of repairing and maintaining the dams. Now, a century after their construction, the wilderness lake dams need removal or rehabilitation, according to a 2018 study.
The study recommends the decommissioning of most of the dams, but lists a couple with the largest storage capacities as good candidates for rehabilitation. The study also states that rehabilitated dams at the larger lakes could store spring runoff and release it for late-season flows in Rattlesnake Creek, which could help bull trout, a threatened species protected under the Endangered Species Act.
Rattlesnake Creek provides important habitat for trout, especially native bull trout and cutthroat trout, which need cold water.
“One of the main indicators of whether a bull trout is going to survive in a creek is how cold the water is,” said Ladd Knotek, fisheries biologist for Montana Fish, Wildlife and Parks. “We are seeing really rapid increases in stream temperature in many places throughout the bull trout’s historic range and that seems to be the main driver of bull trout decline.”
Last year was Montana’s driest in more than two decades. As water temperatures continue to rise, maintaining cold water habitat will be increasingly important for supporting native trout populations.
Knotek said rehabilitating the larger dams could be “one of the best opportunities that we have if we want bull trout to survive in a place like Rattlesnake Creek.”
Rattlesnake Creek is a vital tributary for both native and nonnative fish in Missoula. Native fish such as bull trout, Westslope cutthroat trout and mountain whitefish — and nonnative but wild brown trout, rainbow trout and brook trout — hatch and spend their first year of life in Rattlesnake Creek before swimming out to the Clark Fork River.
“Literally any fish you catch in the Clark Fork River within five miles of Missoula, there’s a very good likelihood that it came from Rattlesnake Creek,” said Rob Roberts, project manager with Trout Unlimited.
Rattlesnake Creek is poised to remain an important habitat for native trout after the removal of the Lower Rattlesnake Dam last year. The Lower Rattlesnake Dam removal was a collaboration between the city and outside organizations such as Trout Unlimited, the Watershed Education Network and the Montana Department of Fish, Wildlife and Parks.
The removal of the Lower Rattlesnake Dam helped restore habitat for native and threatened fish species. A little over a year after the completion of the project, it’s too soon to have hard data on the benefits of the removal, but Roberts has already seen trout spawning above the former dam barrier.
Now, the city is in the early stages of evaluating different options for the aging wilderness dams, which could include decommissioning some or all of them, reconstructing some dams in order to store water, or improving the dams to meet U.S. Forest Service standards.
From a fishery restoration perspective, rehabilitating the dams at Big Lake and Sanders Lake could increase streamflows and potentially cool the stream temperature later in the summer.
Because the lake dams sit near the top of the mountain where the elevation is steep, they don’t block any Rattlesnake Creek fish migration, though some of the dammed lakes contain nonnative fish that were stocked several decades ago.
The dams at Big and Sanders lakes are the biggest and deepest of the lakes in the Rattlesnake Wilderness. And the city of Missoula owns the rights to use all of that water.
The idea being floated by FWP biologists and Trout Unlimited is to rebuild one or both dams to release water to both augment streamflow in Rattlesnake Creek and buffer the stream temperature.
That would involve rebuilding the outlet dam and the outlet levee to raise the water level in the lakes.
“Think of it as a big bathtub,” Knotek said. “You’re basically trying to maximize the level and the size of the bathtub you have so that you can use those flows and grab colder water from deeper in the reservoir.”
FWP has already done test releases that have shown the ability to increase streamflow with water from the reservoirs. Now, the questions are if water from the reservoirs can be used to cool the stream temperature, and for how long the stream could be cooled.
“The problem is that the infrastructure that’s up there right now is old and kind of dilapidated, so we can’t take water from deeper in the lakes to see what the actual temperature benefit would be,” Knotek said.
Removing or rehabilitating the wilderness lake dams would be a lengthier and more complicated process than the removal of the Lower Rattlesnake Dam because the dams are owned by the city, but are in a designated wilderness area, which presents unique challenges.
For example, any action the city takes on National Forest land outside the easement areas for the dams requires the involvement of the U.S. Forest Service.
It’s also cheaper to decommission the dams than to rehabilitate them, and because they are city-owned, taxpayer money would pay for the project, in addition to funding that could come from grants or organizations.
According to the 2018 study, it would cost an estimated $1.3 million to rehabilitate the dam at Big Lake, compared to about $400,000 to decommission it. Rehabilitating the dam at Sanders Lake would cost an estimated $1.17 million, compared to about $159,000 in decommissioning costs.
Logan McInnis, the city’s deputy director of public works, said the city has a lot to consider, such as cost, community needs and approval, regulatory requirements, environmental impact, water rights and climate change.
McInnis said that everything is currently in the concept stage, though the city is already working with Trout Unlimited on a pilot project to decommission, or remove, a dam at McKinley Lake.
Roberts said that project, which is tentatively planned for the summer of 2023, will demonstrate how work on the dams can be done in a way that’s cost-effective and meets regulations.
“It kind of sets the stage for how the city evaluates what they want to do with the rest of the dams up there,” Roberts said.
This article was originally posted on Could rehabbing dams in the Rattlesnake Wilderness help native trout struggling with climate change?