GLEN — Brian Wheeler, clad in sandals instead of waders, nearly trod on a rattlesnake one day near the Kalsta Bridge.

Ever since, this stop on Wheeler’s water-quality sampling journey along the Big Hole River has been his least favorite.

In the spring of 2020, the Montana Department of Environmental Quality approved the Big Hole River Foundation’s water-quality sampling program. Wheeler, the foundation’s executive director, typically collects data from April through October at seven sites along the river and at three primary tributaries.

He was back out Aug. 12, approaching the task with a clear emphasis on collecting valid data.

“It has to be done in a particular order and a particular way,” Wheeler said.

Three days later, Kyle Flynn, Ph.D., installed two water-quality sensors, known as “sondes,” in the Big Hole River near the Jerry Creek Fishing Access Site.

“We see this as a baseline assessment (of water quality),” Flynn said. “What I’d like to see done is like a weight-of-evidence approach. So, what do we think, if anything, is impacting the fishery? And then the next step is (determining) what can be done about it.”

Bob Seger sang about “workin’ on mysteries without any clues.”

Mystery currently reigns in the Jefferson River Basin about the causes driving the historic declines in trout numbers.

To date, questions loom larger than clues. But clues do exist. They range from the piscatorial effects of low flows and warm water temperatures to the impacts of dissolved oxygen-depleting algae. They range from an out-of-whack pH that could affect a fish’s mucous membranes to the stress on fish of catch-and-release angling.

One variable almost certainly is climate change.

And on and on and on.

Identifying the salient drivers of the decline will likely hinge in the short-run on water quality data.

Flynn installed a total of eight sondes in the Big Hole, Beaverhead, Ruby and Jefferson rivers to monitor late-season conditions and inform initial analyses about how water-quality variables might be influencing declining trout populations in southwest Montana. He said the sites for the sondes were generally co-located with river reaches where Montana Fish, Wildlife and Parks has conducted fish population estimates.

Each sonde will collect about a week’s worth of data during the low-flow, dog days of August.

“Once we’re empowered with data, we can help guide policy solutions to build resiliency for our wild trout populations,” Flynn said.

Wheeler is collecting the Big Hole River Foundation’s fourth year of data, sampling for such things as dissolved oxygen, pH, conductivity, turbidity, water temperature, total nitrogen, total phosphorous and more.

In late September, he also does sampling of aquatic macroinvertebrates, which are insects that live in the water.

“The data can help narrow down where the problems are on the landscape,” he said, helping to identify and prioritize where beneficial projects could go.

The nonprofit Big Hole River Foundation launched water-quality sampling with a pilot project in 2019 after recognizing that no other entity or agency was doing this work.

Wheeler drives his Toyota pickup on the sampling runs and then typically delivers the results to a lab in Helena. He can log more than 600 miles per outing.

Flynn owns KF2 Consulting, based in Helena. Described as a water-quality modeling expert, he was hired by Save Wild Trout as its lead scientist. The new nonprofit formed as concerns soared about declining populations of trout in rivers in the Jefferson River Basin and close observers of the decline felt state officials weren’t reacting with sufficient urgency.

On Aug. 2, Gov. Greg Gianforte traveled to Wise River to talk about declining populations of trout in the Big Hole, Beaverhead and Ruby rivers. He introduced Al Zale, Ph.D., a professor at Montana State University and leader of the Montana Cooperative Fishery Research Unit. Zale and graduate students will initiate research about the rivers’ trout.

“We want to look at things at a number of different stages and times in (the trouts’) lifecycle and try to figure out where the problems are,” Zale said then. “Once we know where the problems are, then we can work at fixing things.”

Wheeler said he is grateful for the research by Flynn and the eventual input from a team put together by Save Wild Trout. Similarly, the work of Zale and students will be valuable, he said.

The goal is to communicate and coordinate, Wheeler said.

“And we’re going to identify whether there are other things we should be testing for,” he said.

Flynn shared similar thoughts.

“The idea really is to have a collaborative effort,” he said.

Meanwhile, at least two fishing guides on the Big Hole River reported recently that the fishing has been good — perhaps, they said, because negative publicity about trout numbers has reduced fishing pressure.