Outflow at the Libby Dam at the south end of Lake Koocanusa will increase as of Thursday, May 13, to aid migration and spawning conditions for endangered white sturgeon in the Kootenai River, near Bonners Ferry, Idaho.
Water managers at the U.S. Army Corps of Engineers, along with federal, tribal and Idaho fishery biologists, said in a statement Wednesday that spring run-off conditions warranted the increased flow from the dam in Montana, just south of the Canadian border.
The operation needs a volume of water to be released from Libby Dam based on the May water supply forecast for Lake Koocanusa, the border-straddling reservoir formed by Libby Dam. The May forecast this year is 5.19 million-acre-feet, or 88 per cent of average. This sets this year’s sturgeon volume at 0.8 million-acre-feet.
“The flow augmentation operation includes increasing outflows to full powerhouse capacity for approximately two weeks to provide river conditions that may increase sturgeon spawning success in the lower Kootenai River,” the statement read.
Outflows will increase on May 13, as Kootenai River tributaries downstream of Libby Dam are forecasted to peak. Discharge from the dam will increase to full powerhouse capacity, about 25,000 cubic feet per second (cfs), and stay at that level for two weeks. Flow will then be dropped to summer flow — no less than 7,000 cfs, which is the bull trout flow minimum associated with Koocanusa’s inflow forecast.
The increased flows are meant to provide river conditions that may increase sturgeon migration to the reach of river upstream of Bonners Ferry, in habitat known to be good for successful spawning, egg hatching and survival of larval sturgeon.
The Libby Dam was built in 1975, on the Kootenai River in northwestern Montana. At 422 feet (129 m) in height and a length of 3,055 feet (931 m), the dam created Lake Koocanusa, the reservoir which extends ninety miles (140 km) upriver with a maximum depth of about 370 feet (110 m). Forty-two miles (68 km) of it are in Canada in southeastern British Columbia.