Selenium in the Kootenai River Basin, Montana, Idaho and British Columbia

Koocanusa Reservoir — also called Lake Koocanusa — stretches 90 miles across the international border, from southeastern British Columbia into northwestern Montana. Selenium flowing into it has been measured at levels above State and Federal standards for water quality and aquatic life. A 2022 U.S. Geological Survey (USGS) fact sheet sets out what is known about the problem and how the agencies involved are tracking it.

The study area. USGS figure.

The basin and the concern

The reservoir lies in the drainage basin of the Kootenai River (spelled "Kootenay" in Canada), which holds critical habitat for native fish. Libby Dam impounds it 16 miles upstream of Libby, Montana.

Selenium is a micronutrient that living things need, but at high concentrations in water it builds up in fish and birds that lay eggs, causing a range of sublethal harm and death. One possible source in this basin is coal mining in British Columbia's Elk River Valley, where bedrock is dug away to reach seams of coal used in steelmaking. Five open-pit coal mines operate in that part of southeastern British Columbia, producing about 21 million tons of metallurgical coal a year.

A, Libby Dam, Montana, 2008 (U.S. Army Corps of Engineers, Seattle District Public Affairs Office). B, mining in the Elk River Valley, 2021 (Travis Schmidt, USGS).

On the Elk River, 2.2 miles above where it empties into the reservoir, a British Columbia monitoring station (site 0200016) has recorded total selenium from below detection to more than 8 micrograms per liter (µg/L) since 1984.

Total selenium in the water column at British Columbia site 0200016 on the Elk River, 1984–2022. USGS figure from British Columbia provincial data.

New limits

Site-specific selenium standards for the reservoir came out of joint work by the USGS, the Montana Department of Environmental Quality, British Columbia's Ministry of Environment and Climate Change Strategy, the Lake Koocanusa Monitoring and Research Working Group, and the Selenium Technical Subcommittee. Montana wrote them into State law in 2020, and the U.S. Environmental Protection Agency (EPA) approved them in 2021. They set 0.8 µg/L for dissolved selenium in the water and 15.1 milligrams per kilogram (mg/kg) dry weight for fish eggs (ovary tissue), alongside standards for muscle and whole-body tissue.

What earlier studies found

Monitoring here goes back to at least 1967, when the U.S. Army Corps of Engineers, which manages the reservoir, and the USGS began sampling water to learn how Libby Dam's operations affect the river below it. Biological surveys were done before and after the dam was built, and the Kootenai Tribe of Idaho, with other agencies and local groups, has worked to restore dwindling fish populations such as burbot. Concern that mine discharge has raised selenium levels has recently brought more monitoring, though more data and analysis are needed to understand how selenium moves through the basin's chemistry and ecology.

Relative abundance of burbot (Lota lota) in Koocanusa Reservoir, 1980–2020. USGS figure from Montana Fish, Wildlife and Parks data.

The basin is critical habitat for white sturgeon, burbot, mountain whitefish, bull trout and genetically pure westslope cutthroat trout, some of them threatened or endangered. In a study with the EPA, the USGS arranged for fish tissue to be tested for selenium during population surveys by the Idaho and Montana wildlife agencies and the Kootenai Tribe of Idaho. In 2018 and 2019 it gathered 142 fish of 13 species between Libby Dam and Bonners Ferry, Idaho. Selenium in most mountain whitefish egg samples was above 15.1 mg/kg dry weight, the level at which reproduction may be harmed. Two kokanee salmon from below Libby Dam carried eggs, with 4.17 to 5.01 mg/kg dry weight.

Montana Fish, Wildlife and Parks later reported that its 2020 samples of peamouth chub, redside shiner and westslope cutthroat trout included higher selenium concentrations than samples from earlier years.

Monitoring now

The Corps of Engineers tracks the reservoir's flow and water quality, and the USGS streamgage at Libby Dam (site 12301933) has logged discharge, gage height and other measures since 1964. In 2019 the USGS began its own water-quality program in the reservoir to serve Tribal, State and Federal regulators in both countries. Its aims are a long-term record of dissolved and total selenium and related substances, and an understanding of what controls selenium's occurrence. Samples and readings such as pH, temperature and dissolved oxygen are taken by hand from time to time and continuously by automated samplers at several depths, mainly at the international boundary (site 12300110), the Libby Dam forebay (site 12301919) and the river below the dam (site 12301933).

USGS staff sampling water quality in Koocanusa Reservoir. Photograph by Ashley M. Bussell, USGS.

Montana's environmental agency, British Columbia's forests ministry, the mining company Teck Coal and others collect data too. The Corps runs three stations on the U.S. side of the reservoir, the province keeps long-term stations on its tributaries, and Teck Coal has monitored physical, chemical and biological conditions upstream and downstream of the Elk River since 2014.

Work ahead

The USGS is building a shared database of environmental data from the many agencies working in the reservoir and on the river between the Canadian border and Libby Dam. Combining them is hard: field and laboratory methods differ, sampling frequency varies, and there are gaps in place and time. The USGS is working through each dataset's quality-assurance records and metadata to reconcile them.

Dissolved selenium measured by the USGS, the Corps, Montana's environmental agency and Teck Coal, using similar methods at sites near the border, 2013–21. USGS figure.

A platform holding a high-frequency sampler and its equipment, 2019. Photograph by Chad Reese, USGS.

It is also running a mass balance of the reservoir: how much selenium arrives from the Elk River and elsewhere, how much leaves through Libby Dam, how much sits in the reservoir, and how that amount changes. A mass balance points to the sources behind water quality, supports modeling, and gives a baseline for seeing how the basin and reservoir respond once control measures are in place.

Sources

• U.S. Geological Survey Fact Sheet 2022–3033: "Selenium in the Kootenai River Basin, Montana and Idaho, United States, and British Columbia, Canada." The fact sheet's references include Montana Department of Environmental Quality rules and technical documents, EPA's selenium criterion, Mebane and Schmidt's 2019 USGS data release, and Montana Fish, Wildlife and Parks' 2021 Libby Dam mitigation report.