The Priest Lake Water Management Study was initiated by the Idaho Water Resource Board (IWRB) to evaluate opportunities for improving operation of the Priest Lake and Priest River system in order to meet long-term management objectives. The study includes:
evaluation of alternatives to maintain required lake levels and river flows through lake operations and increased storage of water in the lake,
potential structural and operational modifications to the Priest Lake Outlet Dam, and
analysis of options to improve access and navigable conditions for the Priest Lake Thorofare.
In accordance with Idaho Code § 70-507, the dam is operated to maintain the lake levels at three feet on the USGS gage for recreational purposes.
Purpose and Objectives
Preservation of lake levels through the recreation season to support the local economy and meet the Idaho Code lake level requirements, and avoidance of negative impacts to downstream river flows.
Maintaining marine access through the Thorofare channel between Upper Priest Lake and Lower Priest Lake.
Priest Lake is located on the Priest River in the northern Idaho Panhandle. It is a significant draw for tourism and recreation in the area and is known for the pristine variety of wildlife, clear and clean water, and recreational fishing opportunities. Lower Priest Lake is approximately 18 miles long, has a maximum depth greater than 300 feet, and has active storage space of approximately 76,000 acre-feet. It is connected to Upper Priest Lake (which is approximately five miles long) by a three-mile long channel known as the "Thorofare," which has been historically and actively used by the public for recreation and access to the upper lake. A 1,400-foot-long breakwater structure at the north end of Lower Priest Lake is intended to manage sediment transported from the upper lake and to provide wave and erosion protection to landowners at the north end of Lower Priest Lake. While the breakwater structure has kept the mouth of the Thorofare open since the early 1900s, its structural decline over the past several decades along with logging operations north of the area have potentially contributed to sand and gravel depositions at the confluence of the Lower Priest Lake. The sedimentation at the confluence has become unmanageable and, at times, prohibits motorized boat access through the Thorofare.
Priest Lake Dam is an outlet control structure which was constructed in 1951 to maintain lake levels in Lower Priest Lake and downstream flows in the Priest River. The dam is owned by IDWR and operated by a contractor on behalf of IDWR. In accordance with Idaho Code § 70-507, it is operated to maintain lake levels at three feet on the USGS outlet gage after spring run-off for recreation purposes. Efforts are also made to maintain a minimum of 60 cubic feet per second (cfs) in the Priest River downstream of the dam. This minimum flow was originally measured at the USGS Priest River Gage near Coolin (Dickensheet gage). However, this gage was decommissioned by the USGS in 2004. The dam is approximately 12 feet high with eleven manually-operated radial gates to regulate discharge and it does not have an emergency spillway.
In 2015, limited water supply and drought conditions in Northern Idaho made maintaining the required summer lake levels and downstream flows in the river difficult. This situation, coupled with concerns about the declining condition of the breakwater structure and Thorofare access issues, elevated interest in developing both operational and engineered improvements to the Priest Lake and Priest River system. In response to these concerns, the IWRB authorized funding to initiate an evaluation of strategies and options to meet the long-term water management objectives of the Priest Lake and Priest River system.