How Glacier National Park's Sentinel Streams Fared, 2007–2019: Warmer Water, Good Habitat

A technician collects water from an alpine stream with snowy mountains behind

Sampling water chemistry at Reynolds Creek in 2011. Photo: NPS/B. Schweiger.

At four of Glacier National Park's sentinel stream sites, water temperature climbed an estimated 1 to 1.5 °C per decade from 2007 to 2019, a large and concerning change. Most of the park's streams are Outstanding Resource Waters in Montana. They hold imperiled bull trout, west-slope cutthroat trout, the threatened meltwater stonefly and almost 50 diatom (algae) species new to science. Protected inside the park, they are still open to indirect stressors such as climate change and air pollution.

How the streams are watched

The Rocky Mountain Inventory and Monitoring Network measures water quality and quantity, streamside habitat, watershed conditions, stressors and how aquatic invertebrates and algae are doing. Park staff handle fish work separately. This article summarizes six “sentinel” streams, hand-picked as “canaries in the coal mine” and compared with two other subsets: randomly selected “survey” sites and hand-picked “gradient” sites.

Map of the Rocky Mountain Network's stream monitoring sites in Glacier National Park, Montana

Stream monitoring sites in Glacier National Park; sentinel sites are marked with yellow stars. Image: NPS.

What they found

Area	Result for 2007–2019
Climate and water balance	Most indicators in poor condition and declining. Climate is the master variable for stream ecology here, and warmer conditions with less available water are predicted.
Human disturbance	Sentinel sites in good condition with no sign of significant change, but visitation is growing. Social trails, trampled vegetation and roads increased near Swiftcurrent Creek.
Water and sediment chemistry	Mostly good, with little change. Chloride and calcium rose slightly at Swiftcurrent Creek, and acidity was periodically high at the alpine Reynolds Creek site. Streambed trace metals rose or were higher than expected at some sites and need more research.
Water temperature	Increased at four sites, driven by climate.
Physical habitat	Largely good and stable. Invasive exotic plants appeared in low amounts in most years at all sites but Reynolds Creek, where the desired condition is zero.
Bioassessment	Good overall, with no increase in the invasive diatom Didymosphenia geminata (didymo) or any other aquatic invasive species at sentinel sites, though more warm-water-tolerant invertebrates showed up.

The chloride and calcium could have arrived as airborne pollutants, washed in during road maintenance, or come from faster weathering of sedimentary rocks. The high acidity at Reynolds Creek may come from airborne nitrates or sulfates from sources outside the park.

Aerial photo of roads, parking and buildings beside Swiftcurrent Creek

Swiftcurrent Creek runs beside a large campground, housing, visitor services and roads. Its upstream tributary, Wilbur Creek, drains much of the developed area.

Why water temperature matters

Water temperature affects the survival of stream life, including the federally threatened bull trout and the aquatic invertebrates at the base of the food web. The monitors saw the effect already: warmer water brought more warm-water-tolerant invertebrates into the mix.

Mayfly adult and caddisfly larvae, warm-water-tolerant invertebrates typical of Glacier National Park

Warm-water-tolerant stream insects typical of the park: a mayfly adult (Diphetor hageni) above and caddisfly larvae (Brachycentrus occidentalis) below. Courtesy USGS/J. Giersch.

Fish and what comes next

Outside the network's program, park staff found concerning patterns in invasive fish. Rainbow and brook trout increased or expanded in tributaries of the Middle and North Forks of the Flathead River, and brook and bull trout hybridization was documented for the first time in the St. Mary River watershed. Didymo still needs watching because not all baseline survey sites from 2007–2009, where it was abundant, have been resampled.

The authors call Glacier's streams largely pristine but not invulnerable. Managers face the challenge of protecting alpine streams where the rare meltwater stonefly lives and of keeping the character of the wild and scenic rivers, and the park's high-quality streams may serve as a reference for land managers restoring more disturbed streams across the region.

Sources

National Park Service, Rocky Mountain Inventory and Monitoring Network, Climate, Water Temperature, and the Condition of Sentinel Streams at Glacier National Park, 2007–2019, prepared by Sonya Daw, Billy Schweiger and Dana Witwicki, and based on the 2024 report by Schweiger and others (Natural Resource Report NPS/ROMN/NRR—2024/2631); rewritten in hubnx's own words.