Drought and Hot Water Spell Trouble for Native Fish

Idaho, like many places across the West, is in drought. The extent depends on location, but almost 60% of the state is in the extreme drought classification. According to Drought.gov, much of Northern Idaho and a large swath of central Idaho are in “exceptional drought,” the highest category. A low winter snowpack that melted off more rapidly than normal, followed by extreme temperatures, has left much of the state hot and dry. Our river systems and lakes are no exception, with this summer’s warm water conditions hurting native fish populations. 

Idaho’s wild salmon and steelhead have had to deal with lethally hot water temperatures in stagnant Columbia-Snake River reservoirs during their migrations upstream. Salmon, cold water adapted fish, begin to shut down and die when exposed to water temperatures over 68°F. Temperatures in the reservoirs have been exceeded 70°F for weeks on end this summer. The fish develop lesions and become diseased before eventually dying, unable to migrate upstream and successfully spawn. 

Warmer water has less oxygen, and when our river systems heat up, they become virtually unlivable for native cold-water fish. To survive, salmon and steelhead have utilized “cold water refuges” - where cold tributary streams flow into the Columbia-Snake - as layovers on their migrations through the hot water reservoirs.

While reservoirs on the Lower Snake have significantly worsened the hot water conditions compared to a free-flowing river, virtually all of Idaho’s river systems experienced much hotter than normal conditions this summer. High temperatures in the Salmon River concerned fishery managers enough to implement a trap/haul program for migrating Endangered Snake River sockeye. The fish, already stressed from their journey through the warm Columbia-Snake reservoirs, were trucked straight to the Eagle Fish Hatchery. 

Silver Creek Preserve closed access to its renowned fishing sites in early July, citing low water and high temperatures. Native trout species, like salmon, become stressed when water temperatures climb. Silver Creek, a spring-fed system, reached 73°F before the closure. Temperatures have now begun to drop, and the iconic trout stream opened to fishing once again on August 11th. 

In neighboring Montana and Oregon, “hoot owl” fishing restrictions were in place on many river stretches through July, essentially closing streams to fishing from 2pm until the following morning. The idea behind these restrictions is to reduce fishing stress on populations that are dealing with hot water. 

Idaho Fish and Game chose not to implement such restrictions, citing the strong resiliency native trout have to wide swings in temperature. The agency argued that short-term restrictions are unlikely to affect populations long term, even during extreme heatwaves. 

The concern is that models show that this summer's hot, dry conditions will increasingly become the norm thanks to climate change. Outdoor recreation, including fishing, has become more popular, meaning that overstressing local trout populations that are coping with heat will increasingly become a possibility. 

Fish managers focus on habitat restoration actions that make stream channels deeper and more shaded by vegetation to better retain cold water conditions during droughts. Downstream habitat is just as crucial as headwater and spawning habitat, especially for far migrating salmon and steelhead that utilize 900 miles of river on their ocean migrations. Ensuring our wild trout and salmon have access to cold, free-flowing river habitat is an organizational priority at Idaho Rivers United.