By Jack Buban EBS GUEST COLUMNIST
If you want to understand the true health of a living river, look past the sweeping mountain vistas and the rising trout on the surface. Look underneath the riverbed rocks. There, clinging to gravel and submerged wood, live the aquatic macroinvertebrates—mayflies, stoneflies, caddisflies and midges—that form the foundation of the Gallatin’s ecosystem.
These tiny creatures are ecological storytellers. Because different aquatic insects have varying sensitivities to water temperature, flow rates, fine sediment and dissolved oxygen, their presence serves as an immediate barometer for water quality and overall river integrity. Without a healthy and diverse insect population, the fish and wildlife that depend on the river simply cannot thrive.
The Gallatin River Macroinvertebrate Monitoring Program completed its second full year of field sampling in 2025, tracking these aquatic insects to better evaluate ecosystem health, water quality and the future of the river’s trout population. The program’s core objectives focus on tracking insect abundance over time, evaluating environmental influences like dewatering and sediment and engaging local volunteers through hands-on stream monitoring. Building upon the initial baseline report established in 2024, the latest findings provide a valuable snapshot of the current ecological health of the Gallatin.
The 2025 dataset revealed several encouraging signs, and a healthy bug population indicating benefits both for local anglers and the overall ecosystem. At most monitoring sites, densities of “good bugs”—specifically mayflies, stoneflies, and caddisflies—exceeded an impressive 1,000 individual insects per square foot. In total, insect abundance measured nearly 3,000 insects per square foot, almost three times those on the Madison River and comparable to levels on the Henry’s Fork River in Idaho.
This abundant food base confirms that the river continues to support many of the hatches that make the Gallatin a renowned blue-ribbon fishery. Furthermore, a basic visual comparison between 2024 and 2025 shows a slight increase in the relative abundance of these key trout foods, paired with a noticeable decline in midge abundance. Sensitive indicator species like salmonflies and golden stoneflies continue to hold strong in key reaches, signaling pockets of well-oxygenated, high quality water where trout can thrive.
Despite these positive numbers, the latest report also highlighted ongoing signs of ecological stress that warrant close attention. Aquatic insect communities still contain relatively high proportions of pollution-tolerant organisms and non-insect species, which are frequently associated with excessive algae growth and reduced oxygen levels.
Most surprisingly, the upper reaches of the Gallatin—including sections just downstream of Yellowstone National Park and above the confluence of Taylor Creek—exhibited lower ecological integrity than the lower sections of the river. Because there is minimal human development in the upper watershed, this unexpected finding underscores the need for continued monitoring to isolate the underlying environmental drivers behind this stress.
Ultimately, drawing firm conclusions from a two-year dataset is challenging, as multi-year monitoring is essential to distinguish brief natural fluctuations from long-term ecological trends. Ongoing data collection will be critical to answering the core question on everyone’s mind: are the river’s insects declining or thriving, and what does that mean for the Gallatin as a whole?
Protecting a gem with such immense socioeconomic and environmental value requires collective, community-driven stewardship.
The Gallatin River Task Force, The Salmonfly Project and Gallatin River Guides are hosting an educational Entomology Clinic on Aug. 25, where participants can get up close with the river’s insects.
Volunteers are also needed for the broader 2026 field sampling season taking place from Aug. 24 through Aug. 28. These opportunities are offered to help build this crucial long-term dataset, and to give community members hands-on experience during the upcoming 2026 monitoring season. Further details and registration information are available on the GRTF website.
Jack Buban is the community engagement manager at the Gallatin River Task Force.
