Priest River Fish Kill

By JAMES LEA, SCA board member

"The challenge will be to provide more and colder water to the downstream river to help satisfy the requirements of the river constituency."

This summer of 2021, temperatures in the lower Priest River became dangerously high and stream flows exceptionally low. This resulted in fish kills affecting cold water species such as mountain whitefish, cutthroat trout and char. The causes are multiple. Part of the problem is related to our warming climate. Over the last 100 years there has been substantial increase in temperature, averaging about 2 degrees F, much of this occurring in the last 30 years. (See Sightlines’ online archives for the Spring 2019 issue, which analyzes over a century of data from the Priest River Experimental Forest weather station.) This trend is not likely to reverse.

Another part of the problem is human caused changes to the environment. In the mid-20th century, the lower river was used to drive logs down to the mills in Priest River. This resulted in scouring of the river bed with loss of deep holes and structure where fish can take refuge.

In 1950, the Idaho State legislature enacted legislation authorizing the building of a dam about 2/3 mile downstream from Outlet Bay. The site of the dam is just downstream from Match Bay where logs historically were held in pens awaiting the spring run-off. The purpose of the dam is to regulate the waters of Priest Lake to preserve for the use of the people the beach, boating and other recreational facilities. A wooden dam was built in 1951 with control delegated to the State Reclamation Engineer. The act was amended in 1957 with the stipulation that the level of the waters be maintained at 3.0 ft on the USGS outlet gauge during the summer recreation season. Between September 10 and October 31, the lake could be drawn down as determined by the Reclamation Engineer. In 1961 another amendment eliminated the dates of the draw down and left it to the discretion of the Reclamation Engineer specifying only that the draw down should occur after “the main recreational season”. For many years the recreational season has been defined as from Memorial Day to Columbus Day. The original dam was replaced in 1978 and is currently being upgraded to raise the level safely to 3.5 feet, authorized by statute in 2018. Also, at this time the ownership of the dam was assigned to the Idaho Department of Water Resources. With the elevation of the lake water during the summer many lakeshore properties became more readily accessible by boat. Likewise, there has been improved access to resorts and marinas. From Outlet Bay to the dam, river property effectively became seasonal lakeshore property with easy access to the lake proper during the summer.

As often happens yesterday’s solution becomes today’s problem. In 1950 no one could possibly have anticipated the potential impact of the dam on the lower river. At the time there was no such thing as an environmental impact statement. Ecology was a concept familiar only to specialists. Aldo Leopold’s A Sand County Almanac had only been published in 1948. No one at that time could have possibly conceived of a thing called global warming. In spite of the best intentions the dam has now created problems for the lower river and its fishery.

In 2015 the flow of the river was completely stopped for two days, turning the river into a disconnected string of stagnating pools. As it stands now the river is being managed to hopefully maintain a minimum flow of 60 cfs; however, the IWRB does not have legal authority to lower the lake level below 3.0 ft during the summer recreational season. This means that there will be times in the future when the dam may be closed and the river flow at the outlet will cease. There are 39 property owners downstream who have water rights for irrigation and domestic use. The Idaho Department of Water Resources itself has the largest claim for the purposes of recreation and wildlife. This claim is for 700 cfs from 7/1 to 7/31 and 300 cfs from 8/1 to 10/31. In addition, the IWRB has a responsibility to protect the rivers of Idaho with outstanding fish, wildlife, recreational, aesthetic and geologic value identified and assessed for state protection in the Comprehensive Water Plan. Priest River has been determined by the state to be a highly valuable waterway and is listed as protected under the Idaho Comprehensive State Water Plan for recreation and wildlife. Idaho Fish and Game has determined that the minimum recommended rearing flow for adult and juvenile cutthroat trout and adult rainbow trout is 200 cfs during the period of August 1 to October 31. The optimal rearing flow for adult trout during this period is 400 cfs.

Quite clearly there are competing claims for water with a statute requiring maintenance of a fixed summer level regardless of stream flow yet with downstream users legally entitled to a steady flow of water in the river. Construction of the dam may have also caused increased temperatures in the upper layer of water at the dam where water is spilled; that is to say, increased temperatures relative to prior to dam placement. The dammed upper reach of the river is shallow, broad and sun exposed. Prior to dam placement, water from the warmer lake epilimnion flowed from the lake into the river, but within 1000 yards received cold water input from the west side aquifer and Lamb Creek. This issue may be addressed by a limnological study to be released this fall. Ironically these competing claims for water have created an old-fashioned Western water rights fight here in North Idaho where we are surrounded by inland temperate rain forest.

Moving forward it seems inconceivable that the summer lake level could be altered given the enormous private and business investment in the status quo. The challenge will be to provide more and colder water to the downstream river to help satisfy the requirements of the river constituency, which include property owners, fisherman, paddle craft enthusiasts, and Priest River businesses. Elevating the summer level by 6 inches may help with stream flow but not temperature. Historically the fall drawdown was mandated to start as early as Sept 10. Going forward IDWR could begin spilling water over the dam in September after the water cools to 66 degrees F during the Dolly Varden spawn. With a gradual draw down increased flows could be ensured throughout the early fall. Providing for cool abundant water in the hottest days of summer will prove a more significant challenge.

Original article link here: https://scawild.org/newsletters/SL_Fall_2021.pdf