Libby Dam has been releasing water over its spillway this week to test possible benefits to white sturgeon spawning in the Kootenai River near Bonners Ferry, Idaho.

The “spill test” actually started on June 4, but releases from Libby Dam had to be substantially curtailed because last week’s heavy rains caused the Kootenai River to swiftly rise to flood stage at Bonners Ferry.

The spill test resumed Sunday with Libby Dam releasing water at powerhouse capacity of 26,000 cubic feet per second, plus up to 10,000 cfs over the dam’s spillway. That operation was expected to continue through Saturday.

After that, up to 2,000 cfs may be spilled to maintain enough storage space behind Libby Dam because the U.S. Army Corps of Engineers is expecting a significant runoff from an above-average mountain snowpack above the Kootenai Basin.

This is the second year for a spill test on the Kootenai River, with multiple agencies trying to determine if the maximum flows have any influence in improving white sturgeon spawning success.

The hope is that higher flows will encourage adult sturgeon to swim into optimum spawning habitat in a stretch of river called the “braided reach” upstream from Bonners Ferry.

Spill operations are called for in a 2006 U.S. Fish and Wildlife Service Biological Opinion for white sturgeon, which are protected as an endangered species.

In addition to tracking the movements of sturgeon tagged with radio transmitters near Bonners Ferry, agencies are monitoring the impacts of spill operations on bull trout and other fish in the river just below Libby Dam. Spill raises dissolved gas levels in the river, with the potential to cause gas-bubble trauma in fish.

In other dam-related news, load limits on the Bonneville Power Administrations power grid played a part in reducing generation at Libby and Hungry Horse dams between June 7-9. Water releases had to be reduced to cut 20 megawatts of generation at each dam because power loads in the Flathead Valley dropped off and the amount of power that needed to be transmitted from the dams exceeded limits on transmission lines.

“Unless have a place to put the power, you can’t generate without overloading the system,” said Joel Fenolio, a spokesman with Corps of Engineers in Seattle. “There wasn’t enough load in the Flathead Valley to accommodate both Hungry Horse and Libby generation.”

Fenolio said he expects emergency generation reductions to become more common because of additional wind power generation that is connected to the BPA grid, mostly from sources in Washington.

“When they generate with wind, they will have to cut back on hydro generation,” he said.

Reporter Jim Mann may be reached at 758-4407 or by email at jmann@dailyinterlake.com.