Living in Eastern Idaho allows me to fish some of the finest trout water in the country, from the South Fork of the Snake to the Madison in Montana. But lately, nostalgia has drawn me south, to northern Utah’s Logan and Blacksmith Fork rivers, both of which flow through the fifty-mile-long Cache Valley where I grew up. Each of these rivers had healthy salmonfly hatches when my grandpa was a kid, but now only the Blacksmith Fork does, and few people seem to know why.
The Logan’s annual salmonfly hatch used to be as large and reliable as nearly any in the West. But this hatch began to wane throughout the ’60s and ’70s; it’s now nearly impossible to find an adult salmonfly anywhere along the Logan. Conversely, the still-robust Blacksmith Fork flows through an adjacent canyon and belongs to the same Bear River watershed.
Two hours south of the Logan, salmonflies have also disappeared along a stretch of Utah’s Provo River, from Jordanelle Reservoir to Utah Lake. Severe declines have also been reported on the Ogden River below Pineview Reservoir.
This case of disappearing salmonflies isn’t just a Utah problem. Over the past sixty years, salmonfly declines have been reported in at least eleven important fisheries in the Rocky Mountain West. Populations have collapsed in more than three hundred miles of river in Montana, including stretches of the Madison (below Ennis Reservoir); the Smith (above Camp Baker); the Yellowstone (just above and below Livingston); and the Clark Fork River above Missoula.
In Colorado, salmonflies have gone locally extinct in parts of the Arkansas River, and from several sections of the upper Colorado (Windy Gap Dam to Kremmling), and the Gunnison, from the town of Gunnison to Blue Mesa Dam. It’s likely that unreported losses have also occurred elsewhere, especially in smaller, less well-known fisheries.
In many cases, these historic populations were incredibly strong. In the 1950s, on the Provo, one research paper reported fifty or more salmonfly nymphs found under a single boulder at sites where now there are none. Unfortunately, all attempts at restoring salmonflies to areas where they had previously gone extinct—including several attempts along the Logan in the 2000s—have been unsuccessful.
Scientists have been trying to determine the cause of these disappearances for years. In most cases, the rivers where declines have occurred still maintain strong trout populations. Likewise, most appear to be healthy: fast-flowing water cascades over boulders or meanders around willows or cottonwoods—seemingly prime habitat. It’s likely that a combination of many subtle changes—temperatures, flows, sedimentation, pollution, and the availability of food—is responsible.
Recent studies show that although salmonflies can withstand surprisingly warm water temperatures (above 80ºF) for long periods, they can die in cooler water when flows and oxygen levels are low or when pollution levels are high. In addition, sublethal impacts can negatively affect nymphs later in life, making it difficult to molt or to time their emergence properly and ensure reproduction as adults. This complexity makes pinpointing the problem especially challenging, particularly when negative impacts differ from river to river.
Scientists do have hypotheses as to why declines have occurred in certain locations. Along the Madison, for example, where low flows have become more common in recent years (recall the Hebgen Dam malfunction in December of 2021), causing water temperatures to spike. And in the Provo, where declines are thought to be related to the combined effects of dams, water withdrawals, agriculture, and urbanization. In the upper Colorado, increased siltation from reduced flows is likely the culprit. These are just a few specifics, though. In most rivers, the true causes of salmonfly declines remain a mystery. It’s been suspected that their extinction on the Upper Logan, for instance, was due to high levels of salt washing into the water. While this has yet to be confirmed, biologists at Utah State University are currently investigating whether salmonflies are sensitive to long-term exposure to salt.
Considering the number of anglers who view the salmonfly emergence as a can’t-miss event, and the economic impact that a healthy hatch can have on local economies, it is surprising how few of these declines have been seriously investigated. Two aquatic entomologists from the University of Montana in Missoula—Jackson Birrell and James Frakes—plan to change that. Birrell and Frakes have formed a nonprofit called The Salmonfly Project (salmonflyproject.org) with the goal of protecting—and, where possible, recovering—salmonflies across their native range. Both are avid flyfishers with scientific backgrounds in the ecology and physiology of aquatic insects, and they use this knowledge to guide their work.
The three goals of The Salmonfly Project: perform ecological surveys and experiments to understand why salmonflies are declining; collaborate with diverse stakeholders to help monitor and track current salmonfly populations; and design and implement restoration and remediation plans based on the science that they and others produce.
The Salmonfly Project is being launched as an ongoing “citizen-science” project, and Birrell and Frakes are asking for the public’s help. “Additional research is vital if we wish to protect remaining populations,” says Birrell. “And we need data from anglers across the West to help us identify areas where salmonflies have declined, or potentially rebounded.” Visitors to their website can fill out a “stakeholders’ questionnaire.” (And of course, make a charitable contribution if they feel so inclined.)
“We are living in an era when the natural world, from polar bears to steelhead to salmonflies, is being strongly influenced by human activities,” says Birrell. “Salmonflies are on an unfavorable trajectory, and we’d like to do all we can to correct that.”