Average water temperature: The John Day reservoir reached a high average temperature of 70.34°F on September 4.

Disastrous Return for Snake River Sockeye
By Miles Johnson, Legal Director, Columbia Riverkeeper and
Stephen Pfeiffer, Wild Fish & Hydropower Policy Manager, Idaho Rivers United

Sockeye migration to Stanley Basin was awful in 2026, despite cooler weather conditions and cold water releases from Dworshak Reservoir attempting to aid survival through the hydrosystem. The reason likely has to do with poor conditions upstream on the Salmon River in late summer, which provided no relief to the already thermally stressed sockeye after they moved out of the hydrosystem. Hot water exposure continues to threaten the survival of endangered Snake River sockeye.

Once again this year, only a few endangered Snake River adult sockeye salmon have successfully swam back to their spawning areas in the headwaters of the Salmon River, near Stanley, Idaho. 2026 saw a low overall return of sockeye to the Columbia River Basin, with an estimated 463 adult endangered Snake River sockeye passing Bonneville Dam (the first of eight dams on their upstream migration route). This was lower than expected, and low relative to the last several years.

Adult Snake River sockeye migrating upstream this summer encountered warm water temperatures that were often above the 68°F threshold that has been determined for safe salmon and steelhead migration. Due to relatively favorable weather in late June and July, water temperatures remained lower than expected—despite the continued status quo operation of eight large mainstem dams on the lower Columbia and Snake rivers. Although this “best-case” weather scenario occurred, many Snake River sockeye succumbed to hot water, and overall in-river migration success was poor in 2026. Read on for details and take-aways.

Water and weather during the 2026 sockeye migration.

Mother Nature did her best to help returning adult sockeye migrate through the lower Snake River reservoirs in 2026. This summer saw relatively few days where the air temperature exceeded 100°F and we experienced short heat waves; these conditions helped keep the water cooler than in past summers when heat domes or heat waves occurred.

Additionally, the Army Corps expanded its past use of water releases from Dworshak Reservoir to cool the lower Snake River during peak sockeye migration. In 2026, federal agencies made a new plan to release more water from Dworshak Reservoir, with the goal of keeping the lower Snake River at Lower Granite Dam at or below 66°F from July 1 to July 16. The additional water releases from Dworshak to protect sockeye in 2025 and 2026 appear to be partly in response to the threat of litigation by Columbia Riverkeeper, Idaho Rivers United, Idaho Conservation League, and the Northwest Sportfishing Industry Association.

One unexpected rainstorm in late June significantly increased the amount of Dworshak water available for release to aid salmon downstream in the Clearwater and lower Snake rivers in 2026. The unseasonable storm forced the Army Corps to begin releasing cold water before July 1 and also kept the reservoir full later into the summer. Because Dworshak holds a limited amount of cold water—which is used to help both sockeye in July and fall Chinook in September—the Army Corps often limits water releases even when river temperatures in the lower Snake are harming sockeye. However, this year, the combination of relatively cool air temperatures and unexpected summer rains meant that there was enough water in Dworshak Reservoir to meet the Army Corps’ temperature goals for the lower Snake—without drawing down Dworshak Reservoir to levels that could negatively impact fall Chinook.

Many endangered sockeye still succumbed to hot water in the lower Snake River in 2026.

Unfortunately, the Army Corps’ temperature goals (even when unusual weather allows them to be met) are not sufficient to protect endangered Snake River sockeye from significant mortality and cumulative thermal stress. This is because the Army Corps sets its temperature targets at Lower Granite Dam (the furthest-upstream dam on the lower Snake). As the river flows downstream through the remaining 100 miles of the lower Snake River, the reservoirs elevate water temperatures to levels that are unhealthy for salmon and steelhead. While water releases from Dworshak Reservoir helped keep the river relatively cool in the Lower Granite Dam reservoir in 2026, temperatures downstream at the other three lower Snake River Dam reservoirs exceeded 68°F in early- to mid-July and remained above this threshold for the rest of the sockeye migration season.

Snake River sockeye experienced thermal stress in 2026: Roughly 30 percent of tagged fish did not survive their migration from Bonneville Dam through the lower Snake River, and fish managers noted a significant decline in the survival rate of sockeye that migrated later in the summer when the water was warmer.

Sockeye Returns to the Stanley Basin

Due to these routine hot water conditions, fisheries managers face a balancing act every summer between taking the precautionary measure of collecting returning adult sockeye at the upstream end of the hydrosystem near Lewiston (ID), or leaving the fish in the river to naturally migrate the full 900 miles home to the lakes at the headwaters of the Salmon River in central Idaho.

Fisheries managers prefer that sockeye complete their life-cycle entirely in the river. This ensures that the genetic fitness of these hardy fish is passed on to the next generation.

However, with hot water impacts now common for Snake River sockeye, the Idaho Department of Fish & Game and the Nez Perce Tribe frequently trap adult fish at Lower Granite Dam and artificially truck them to a hatchery in Eagle, Idaho, for either release into their spawning lakes or incorporation into the hatchery production. As long as the lower Snake River dams remain, this emergency action is necessary to preserve Snake River sockeye’s unique genetics in the face of a warming climate.

The fish that are collected by fisheries managers at Lower Granite Dam are early migrants, part of a pool of fish with a much higher chance of survival in the river due to lower water temperatures in the early summertime. For fish reaching Lower Granite after roughly the third week of July, survival rates plummet in the upstream stretch between the Lower Granite Dam reservoir and their Stanley Basin spawning grounds in central Idaho.

So far, just 8 endangered Snake River sockeye have made it back to the Stanley Basin this year. While additional fish may continue to show up through early to mid October, the bulk of this year’s migration has been abysmal.

• 333 sockeye made it to the upstream-most dam, Lower Granite.
• 43 fish were removed from the river during its trap/haul operation.
• 290 fish swam on
• Just 3% of these fish have successfully made the final 400 miles of their journey into the Stanley Basin lakes.

Poor survival was likely more pronounced this year due to low flows and high water temperatures in the Salmon River in August and September.

Conclusion:

What all of this means is that sockeye salmon migrating home are increasingly not able to catch a break. A NOAA report from 2015 found that the greater cumulative exposure to hot water in the hydrosystem, the lower sockeye survival was in the free-flowing river upstream of the hydrosystem.

This migration season, exposure to hot water in the reservoirs was stacked on top of poor river conditions upstream, and resulted in a disastrous return of sockeye to central Idaho. 

READ PAST ISSUES OF THE HOT WATER REPORT

The Hot Water Report is a project of: Save Our wild Salmon Coalition, Association of Northwest Steelheaders, Columbia Riverkeeper, Earthjustice, Idaho Conservation League, Idaho Rivers United, National Wildlife Federation, Northwest Sportfishing Industry Association, Orca Network, Pacific Rivers, Sierra Club, and Snake River Waterkeeper.

Data Sources: The 2026 water temperature data for the lower Snake River and lower Columbia River presented in the Hot Water Report are collected from the USGS, and the Columbia River DART program by Columbia Basin Research, University of Washington, with data courtesy of the U.S. Army Corps of Engineers (USACE). These data temperatures are provisional. The 10-year average water temperature data is courtesy of the Fish Passage Center and Columbia River DART program. Water temperature data is provisional. Graphs and tables are assembled by SOS Staff.