Priest River: North Idaho's Next Premier Trout Fishery?

For years, Idaho Department of Fish and Game (IDFG) has been exploring options to improve Priest River’s trout fishery and provide more angling opportunity. Their solution may be found near the bottom of Priest Lake.

In the heat of summer, the 45 mile stretch of water between Priest Lake and the Pend Oreille River cannot support native coldwater fish species such as westslope cutthroat and bull trout. These species prefer temperatures between 43-61°F and the EPA recommends a maximum seven day average of no greater that 65°F(EPA2003)

Unfortunately, summer water temperatures often soar above these thresholds. Water temperatures for the Priest River in August and September ranged from 63-72°F(Berger et al. 2014, Isaak et al. 2017), forcing the few remaining fish to seek refuge in cooler tributaries flowing into the Priest River. The Priest River is even 303(d) designated “water quality impaired” under the Clean Water Act due to high summer temperatures. If the cold-water bypass project is implemented, this could all change.

The current concept would involve a hypolimnetic gravity withdrawal system, essentially a really long pipe that extends into Priest Lake and pulls cold water from far below the surface in the hypolimnion (deep, cold water in the lake), and replaces a portion of the lakes warm outflow with this cold water. The result would be much cooler water temperatures (up to 18°F cooler at the mouth and nearly 2°F at mile 45!) in Priest River, enabling coldwater fish species to live there all year.

Priest River Coldwater Bypass Alternatives Assessment IDFG 2019

To a trout fisherman this sounds like a great idea, but there were several concerns from the public about what a project like this could have on their beloved Priest Lake. Recently, IDFG hosted a virtual public meeting to discuss exactly that. In 2020 Advance Eco-Solutions did a limnological threat assessment of the proposed Priest Lake water release system and reported their findings there. They concluded that the proposed concept would have little to no effect on Priest Lake.

While it is still early and this is only a concept that IDFG is exploring, it does look promising. The Priest River in North Idaho could once again become a premier trout fishing destination.

References Cited

Berger, C., S. Wells, and W. Xu. 2014. Priest River Model: Model Development, Calibration, and Scenarios Report. Water Quality Research Group. Department of Civil and Environmental Engineer and Computer Science. Portland State University. Portland, Oregon.

Isaak, D., S. Wenger, E. Peterson, J. Ver Hoef, D. Nagel, C. Luce, S. Hostetler, J. Dunham, B. Roper, S. Wollrab, G. Chandler, D. Horan, and S. Parkes-Payne. 2017. The NorWeST summer stream temperature model and scenarios for the western U.S.: A crowd-sourced database and new geospatial tools foster a user community and predict broad climate warming of rivers and streams. Water Resources Research. DOI:

EPA (United States Environmental Protection Agency). 2003. EPA Region 10 Guidance for Pacific Northwest State and Tribal Temperature Water Quality Standards. EPA 910-B[1]03-002. Region 10 Office of Water, Seattle, Washington