Priest Lake drawdown date set

PRIEST LAKE — The drawdown of Priest Lake is set to begin Oct. 1, lowering the lake's level below 3 feet, the Idaho Department of Water Resources has announced.

The announcement follows the first full summer after the completion of the Priest Lake Outlet Dam in spring 2024, according to IDWR officials on the department's website. Among the modifications at the dam was an increase of 6 inches to all 11 gates at the dam, completed in spring 2022.

That gives officials additional flexibility to raise the lake by up to 6 inches if needed in drought conditions and will replace the "apron" on the downriver side of the dam to prevent scouring, which can destabilize the dam's foundation.

"With the gate height increase, it is now physically possible to hold the lake level at 3.5 feet during the recreation season," officials said.

Storing additional water in Priest Lake in the spring also allows for additional water flows later in the year to maintain the 3.0-foot lake levels and provide more water for resident fish populations below the dam, IDWR officials said previously.

The work follows a 2018 update to Idaho Code which stipulates that the late will be held between 3 and 3.5 feet during dry and marginally dry years and at 3 feet in wet to normal years.

"The dam modifications and corresponding statute revisions were developed to avoid a repeat of the summer of 2015, in which drought led to extreme conditions," IDWR officials said. "That summer, to maintain the required minimum lake level of 3.0 feet, the flow to Priest River below the dam was reduced to 42 (cubic feet per second). Stakeholders found such low flow in the Priest River to be unacceptable."

To prevent a similar situation, officials decided to maintain the lake at a higher level during the recreational season. The result was the approval of the Outlet Dam construction project and reconstruction of a breakwater structure at the mouth of the Thorofare at the north end of Priest Lake.

"In other words, keeping lake levels higher earlier in summer facilitates preservation of higher flow in the Priest River throughout the summer," officials said.

While the increased gate height has been in place for several years, IDWR officials said the department is still developing best practices for the lake. 

"As you may be aware, weather and environmental conditions vary significantly from year to year at Priest Lake, and lake operations must accommodate the variation," officials said. “Considering weather and environmental variations, along with the newer gate height modifications, the department continues to develop best practices for managing lake levels.”

Toward that end, department officials said they welcome feedback from the public to help decide future operations, planning and creation of best practices at Priest Lake. They invited the public to keep them informed, sharing photos and dates of the lake, especially during dry and marginally dry water years.

Information: northerninfo@idwr.idaho.gov or 208-762-2800