Because of record rainfall, Libby Dam has been spilling water to prevent Lake Koocanusa from reaching full pool — but the increased releases have contributed to the Kootenai River surpassing flood stage at Bonners Ferry, Idaho.

“Basically we are running out of room” in Lake Koocanusa, said Scott Lawrence, a public affairs specialist with the U.S. Army Corps of Engineers in Seattle.

For the month of June, 4.39 inches of rain has been measured at Bonners Ferry, which is more than 260 percent of the average rainfall for the month. The previous record for the month was 3.96 inches, set in 1981.

Corps officials expected the most recent storm to add .5 to 1.5 inches across the Kootenai Basin by the end of Tuesday.

Lake Koocanusa rose 1.2 feet in just two hours Tuesday afternoon, despite the dam operating at powerhouse capacity of 25,000 cubic feet per second, in addition to releasing 15,000 cfs over the dam’s spillway.

Inflows to the reservoir have been about 75,000 cfs, compared to the maximum total outflows of 40,000 cfs.

Lake Koocanusa was about five feet from its full pool elevation of 2,459 feet by mid-day Tuesday, and the Corps is expecting it to approach full pool by Saturday.

The reservoir’s total inflow for the runoff period has reached about 3.3 million acre feet — the third highest volume in the last 50 years.

Earlier this month, the Corps conducted a weeklong spill operation to test potential benefits of higher flows to spawning white sturgeon near Bonners Ferry. When the spill test ended June 17, spill flows were reduced to about 2,000 cfs. But releases over the spillway have been gradually increased for flood control since then.

On Tuesday afternoon, the Kootenai River at Bonners Ferry was a foot above its flood-stage elevation of 1,764 feet because of the high releases from Libby Dam and high inflows from downstream tributaries.

Heavy rains also have caused Kootenay Lake downstream from Bonners Ferry to rise to its highest elevation since 1974.