INTRODUCTION: 
The Hot Water Report provides real-time data in the lower Snake and Columbia river reservoirs to detail the collective impacts of hot, stagnant, and toxic waters on already-imperiled salmon and steelhead. This year’s reports will focus on bringing the data to life, featuring stories from scientists, Tribes, and community members regarding the challenges our Northwest native fish face, and the opportunities to heal their rivers and the ecosystem.

EXECUTIVE SUMMARY:

1. Breaking News: Toxic algal blooms have been detected in the lower Snake River for the third consecutive year. Whitman County Public Health and Garfield County Public Health have issued Health Advisories in response to a water sample testing positive for microcystins, a type of liver toxin that is harmful to people and the river ecosystem, and lethal to pets.
2. Benefits of a free-flowing lower Snake River: Decades of scientific research and current mitigation efforts have consistently demonstrated that restoring the lower Snake River will support healthy salmon populations, restore the ecological function of the river and its surrounding landscape, and provide cooler waters during the summer. In this issue, we highlight some aspects of the cultural importance of rebuilding abundant salmon and the ecological and community benefits of a healthy river and ecosystem.
3. Salmon extinction-in-motion: Take a deep dive with Pat Ford and his special 4-part series in Idaho Capital Sun articles highlighting recent science from and urgent action by the Nez Perce Tribe, Confederated Tribes of the Umatilla Indian Reservation, Oregon Department of Fish and Wildlife, and committed community leaders to prevent salmon extinction and protect salmon endangered by deeply degraded river and stream habitat.
4. Current lower Snake River water temperatures:
   • Highest water temperature in the lower Snake River: Ice Harbor reservoir registered the highest water temperature of 72.95°F on August 17.
   • Total days above 68°F in the lower Snake River: Ice Harbor reservoir has been above 68°F for the longest - at 57 days, compared to 48 days this time last year. 
   • Read current water temperatures in the lower Columbia and Snake rivers here. 

Breaking News: Toxic algal blooms re-emerge on the lower Snake River

Toxic algal bloom seen at the Nisqually John Landing near Lower Granite Reservoir in the lower Snake River on 8/18/2025. © Whitman County Public Health  

Toxic algal blooms have been detected in the lower Snake River for the third consecutive year.

Whitman County Public Health has issued a Health Advisory in response to a water sample taken from the lower Snake River at Nisqually John Landing on 8/18/2025 that tested positive for microcystins, a type of liver toxin that is harmful to people and the river ecosystem, and lethal to pets.

The toxic algal bloom is located intermittently in the roughly 50-mile stretch of river between Nisqually John Landing and Little Goose Dam. Whitman County Public Health reminds residents that blooms occurring in river systems may spread due to wind and water currents, and to avoid areas of water with visible green scum on the surface.

“Warm water and air temperatures, sunny weather, still water conditions, and high levels of nutrients contribute to harmful algal blooms,” states the Health Advisory.

On August 29, 2025, the Garfield County Public Health issued a Health Alert for the presence of a harmful algal bloom in the Snake River 12.7 miles upriver from Central Ferry, near “Rice Bar” towards Lower Granite Dam. Results of the water sample were received on 8/29/2025 also tested positive for microcystins.

“Fishermen and water recreationists are advised to use caution when fishing or boating on the Snake River, the bloom may pose health risks if toxins are ingested or touched,” states Garfield County Public Health.

This summer, all of the lower Snake River dams and their reservoirs have registered high water temperatures between 70°F - 72°F, well over the 68°F “harm threshold” – the biological and legal limit set to protect migrating salmon and steelhead. The lower Snake River dams and their reservoirs are heating the river to dangerous levels each summer and becoming a breeding ground for toxic algal blooms that are hazardous to people, pets, and wildlife.

A sick lower Snake River, where toxic algal blooms are now a regular summer occurrence, increases the pressure on threatened and endangered salmon and steelhead. Already under stress as they migrate through the dams’ warm reservoirs, these coldwater fish must now also contend with oxygen depletion and changes in pH driven by toxic algal blooms, while the reservoirs are at their hottest.

Restoring a free-flowing lower Snake River to protect communities and deliver big benefits to ecosystems and salmon

Removing the four lower Snake River dams will lower water temperatures, allow these cooler waters to flow freely once again and support healthy salmon and steelhead populations. It will dramatically reduce the incidence of toxic algal blooms and support a healthier Snake River overall – one that benefits fish, people, communities, watersheds, and cultures.

We've discussed the challenging river conditions in the first three issues, and we now want to highlight the immense benefits of a restored river in this Hot Water Report series. In this issue, we highlight some aspects of the cultural importance of rebuilding abundant salmon and the ecological and community benefits of a healthy river and ecosystem. Decades of science and many dam removal success stories across the United States demonstrate how restoring the lower Snake River will support healthy salmon populations, restore the ecological function of the rivers and landscape, and provide cooler waters during the summer:

CULTURAL:

• Honoring treaties and legal commitments our nation has made with Tribes: The dams and their reservoirs violate the exercise of Tribal harvest rights by contributing to the decline of salmon runs and wildlife abundance, and blocking access to or altering fishing locations, and, as a result, inequitably impact Tribes’ spiritual, cultural, and physical health. The 1855 treaties negotiated between the United States and the Tribal Nations that now comprise the Confederated Tribes and Bands of the Yakama Nation; Confederated Tribes of the Umatilla Indian Reservation; Confederated Tribes of the Warm Springs Reservation; and the Nez Perce Tribe secured "the right of taking fish at all usual and accustomed places in common with citizens of the Territory,” including on the Columbia River and its tributaries.

  The Department of the Interior, in collaboration and coordination with Columbia Basin Tribes, released a comprehensive “Tribal Circumstances Analysis” in 2024 that outlines the historic, ongoing, and cumulative damage and injustices that the federal dams on the Columbia-Snake River continues to cause to Tribal Nations. The Analysis highlights how the four dams and their reservoirs on the lower Snake River prevent access to 140+ miles of Treaty-protected tribal fishing, hunting, and harvesting of roots, plants, and berries at usual and accustomed streamside locations. 

  The Analysis recommends for the federal government to uphold treaty and trust responsibilities to the Tribes by prioritizing work “to protect these reserved rights and restore associated resources; improving the spiritual, cultural, and physical well-being of Tribes; and advancing environmental justice."

• Recovering historical and cultural areas in the lower Snake River: Beneath the Lower Snake River by National Parks Conservation Association provides a visual map of a few of the rich archaeological, historical, cultural, ecological, geological, and recreational resources that could be restored in a free-flowing lower Snake River. Almost 14,000 acres of land were flooded by the dams and their reservoirs, including over 350 sites, including Indigenous villages, burial grounds, historical towns, landmarks, archaeological sites, recreation areas, river rapids, islands, canyons, and important wildlife habitat.

• Restoring salmon and rivers to improve “spiritual, cultural, and physical well-being of Tribes”: Tribal members carry with them intergenerational trauma caused by actions of the United States government, including the displacement of their peoples from their aboriginal territories and the damming of the rivers. Medical experts and practitioners point to the loss of salmon and First Foods (traditional and balanced diet for the Basin Tribes) as harming the physical and mental health of Tribal members. “The health of the salmon and the health of Tribal peoples are interrelated,” states the Tribal Circumstances Analysis.

  Many of salmon’s nutritional benefits could help prevent and combat health issues that are often disproportionately prevalent in Tribal populations, such as heart disease, diabetes, and mental health challenges. “Restoring salmon restores a way of life. It restores physical activity. It restores mental health. It improves nutrition and thus restores physical health. It restores a traditional food source…”, states a Yakama Psycho-Social Nursing Specialist in the Tribal Circumstances Analysis. “It allows families to share time together and build connections between family members. It passes on traditions that are being lost. If the salmon came back, these positive changes would start.”

ECOLOGICAL:

• Computer modeling confirms a free-flowing river will benefit salmon and steelhead: A computer model by the Environmental Protection Agency shows that removing the four lower Snake River dams would reduce Snake River water temperatures by 6.3°F, on average, during the summer and early fall.

  A published report by Columbia Riverkeeper – ‘White Paper: Computer modeling shows that Lower Snake River dams caused dangerously hot water for salmon in 2015’ – confirms through computer modeling that a “cooler, free-flowing Lower Snake River could provide refuge for endangered sockeye and other salmon that survive the first part of their difficult journey (through the four lower Columbia River reservoirs)”—rather than forcing these fish to migrate through another 140 miles of hot, stagnant, toxic reservoirs. A cooler, freely flowing river will deliver big benefits to migrating juvenile and adult salmon and steelhead - leading to increased survival and reproductive success.

• Repairing healthy habitat for salmon, steelhead, and native fish: Today’s reservoirs and warming waters inundate and destroy diverse micro-habitats that healthy rivers support, including cold-water refuges that salmon and steelhead have historically relied upon during their summer migrations. Without these cold water refuges, fish cannot rest and recover during their long migration.

  In NOAA’s landmark report in 2023, Rebuilding Interior Columbia Basin Salmon and Steelhead, states that breaching the four lower Snake River mainstem dams would transform reservoir habitats back into a river with functional connected floodplains and natural water flow rather than slow-moving reservoir waters. It will re-create favorable river-channel conditions, including island and side channel habitats that support aquatic species. It will also significantly improve “tributary water quality and quantity that would increase the quality of spawning and rearing habitats for both salmon and steelhead.”

• Restoring ecological health to the lower Snake River: Tribal ecological knowledge and studies show that restoring the health of salmon will restore the health and function of the ecosystems they inhabit, and these benefits will extend to more than just salmon themselves, but to many other species as well. Salmon are a keystone species that benefits more than 130 different wildlife species and their landscapes across the Northwest. Healthy salmon populations transport massive amounts of energy and nutrients, such as carbon, nitrogen, and phosphorus, from the ocean to estuaries and freshwater environments.

  “Numbers of returning salmon are not just about salmon. Salmon drive the whole ecology of that population’s geographic area,” states Jay Hesse, director of Biological Services for the Nez Perce Department of Fisheries Resources Management, in an article series about the salmon extinction threshold science and recovery efforts. “Fifty or fewer fish [in a population] signals a total break in that watershed’s ecology, with effects that go well beyond the fish.”

  “Some breakage is visible to us; many fewer bears, eagles, and people hunt the rivers and creeks in season,” writes Pat Ford. “Salmon nutrition for the waters, lands, and life of the territories has been close to nothing for 60 years.” As the health of salmon populations improves, recovery of species and landscapes can be expected to flourish.

• Restoring the lower Snake River is a high priority “centerpiece action”: NOAA's report states, “for Snake River stocks, the centerpiece action is restoring the lower Snake River via dam breaching.” Breaching can address the hydrosystem threat by decreasing travel time for water and juvenile fish, reducing stress on juvenile fish associated with their hydrosystem experience that may contribute to delayed mortality after reaching the ocean, and providing additional rearing and spawning habitat.”

  The Northwest’s endangered fish are running out of time. Given the urgency of the situation facing salmon and steelhead today, NOAA emphasizes that “science robustly supports riverscape‐scale process‐based stream habitat restoration, dam removal (breaching), and ecosystem‐based management, and overwhelmingly supports acting and acting now.”

We all have a responsibility to uphold treaties and commitments made by the United States to Northwest Tribes. We must act urgently to restore healthy and abundant Columbia-Snake River salmon and steelhead by replacing the services and breaching the four federal dams on the lower Snake River. A free-flowing lower Snake River represents a rare and special opportunity to ensure resilient and abundant salmon and steelhead populations thrive for future generations.

Deeper dive into “salmon extinction-in-motion” in Washington’s and Oregon’s Snake River and restoration efforts underway.

The W.T. Wooten Wildlife Area, pictured, spans approximately 17,000 acres. About 17 miles of Washington’s Tucannon River are located within the area’s boundaries, and elevations range from 4,100 feet on Hopkins Ridge down to 1,800 feet on the lowest section of the Tucannon River. (Alan L. Bauer/Washington Department of Fish and Wildlife)We invite you to take a deep dive with Pat Ford and his special 4-part series in Idaho Capital Sun articles highlighting recent science from and urgent action by the Nez Perce Tribe, Confederated Tribes of the Umatilla Indian Reservation, Oregon Department of Fish and Wildlife, and committed community leaders to prevent salmon extinction and protect salmon endangered by deeply degraded river and stream habitat.

The series spotlights the extinction-in-motion of Snake River salmon and steelhead. The 60-mile long Tucannon River flows south into the reservoir behind Lower Monumental Dam on the lower Snake River. Tucannon Chinook are Washington’s only remaining Snake River Chinook salmon population, and they are at serious risk of extinction. The Nez Perce Tribe, the Confederated Tribes of the Umatilla Indian Reservation, and the Washington Department of Fish and Wildlife are translocating them for the years to come to save this salmon population.

Jay Hesse, Director of Biological Services, Nez Perce Tribe's Department of Fisheries Resources Management, says, “We are taking every Tucannon Chinook out of the river, their natural environment. A fish is at great risk when it can’t use its river. And this kind of action also badly strains tribal cultural and harvest connections to the river. But with so few fish, every action we could take now, including doing nothing, has large risks.” As Dave Johnson, the recently retired head of Nez Perce Fisheries, said, “Tucannon spring Chinook are the canary in the coal mine [for Snake River Chinook], and the canary is dying.”

The 2024 status of Snake Basin Chinook and steelhead stocks are dire; however, there is hope for salmon. Restoring a free-flowing lower Snake River and salmon's migratory habitat is essential to recover healthy and abundant salmon and steelhead. Ed Bowles, former Oregon Department of Fish and Wildlife chief of fisheries and salmon adviser to Oregon governors states: “Snake River salmon are facing extinction, population by population. But we also have evidence…that intrinsic productivity is still there in these salmon and steelhead. It is NOT too late.”

Thank you to Pat Ford and the Idaho Capital Sun for publishing this series! Read the full series here:

1. Salmon extinction in motion in Washington’s and Oregon’s Snake River
2. Salmon and steelhead extinction threshold science, and the ocean fish of northeast Oregon
3. The good work underway by Pacific Northwest salmon people in northeast Oregon
4. Last thoughts on salmon and steelhead extinction in the Pacific Northwest

WATER TEMPERATURE DATA FOR LOWER SNAKE AND COLUMBIA RIVERS

Introduction to the water temperature data:

• The Hot Water Report provides bi-weekly updates on real-time water temperatures in the lower Snake and Columbia River reservoirs. We track water temperatures in all eight reservoirs in the lower Snake and Columbia rivers to understand the river conditions that salmon and steelhead must migrate through.
• The daily average and high water temperature data at the eight reservoir forebays are measured with sensors stationed at various depths below the reservoir surface, immediately upstream from the dams.

LOWER SNAKE RIVER WATER TEMPERATURE DATA 8/8 - 8/28

Click here to view the lower Columbia River water temperatures - 2025 Daily Average and 10-year Average.

Average water temperature: Between August 8 - August 28, the highest daily average temperature across all four lower Snake reservoirs was at Ice Harbor reservoir, averaging 72.59°F.

Highest water temperature: Ice Harbor reservoir registered the highest water temperature of 72.95°F on August 17.

Total days above 68°F in the lower Snake River: Ice Harbor reservoir has been above 68°F for the longest at 57 days.

The four lower Snake reservoirs have been above the 68°F (20°C) threshold for an average of 50 days, compared to 43.25 days this time last year.

LOWER COLUMBIA RIVER WATER TEMPERATURE DATA 8/8 - 8/28

Click here to view the lower Columbia River water temperatures - 2025 Daily Average and 10-year Average.

Average water temperature: Between August 8 - August 28, the highest daily average temperature was at the John Day and Bonneville reservoirs, averaging 73.58°F.

Highest water temperature: The John Day reservoir registered the highest water temperature of 74.48°F on 8/28.

DISCUSSION OF DATA:

The end of August marked over 50 days of water temperatures exceeding the 68°F “harm threshold” set to protect migrating salmon and steelhead. All lower Columbia and Snake River dams and their reservoirs have reached temperatures of at least 70°F - 72°F, with temperatures as high as 73°F - 74°F in the lower Columbia River. The dams and their reservoirs are heating much of this river system, making it difficult and/or impossible for adult salmon and steelhead to migrate to their spawning grounds, and for juvenile fish to reach the ocean.

Salmon and steelhead are highly resilient. They can tolerate episodes of warm water, but they also have limits on how long and how much hot water they can withstand. The cumulative impact of hot reservoirs in the lower Columbia and the lower Snake must be addressed quickly - to reduce water temperatures and the overall exposure time for these fish to waters above 68°F.

A collaborative approach between Northwest states, federal agencies, and Tribal Nations is necessary to address rising water temperatures across the basin. Restoring a free-flowing lower Snake River will provide a critical cold-water refuge that salmon and steelhead have historically relied upon to rest and recover during their long upstream migration. A river - rather than reservoirs - will remain much cooler through the summer, especially with cold water infusions released from the Dworshak Reservoir on a tributary to the Clearwater River near Lewiston, ID. With a restored lower Snake River, its significantly cooler waters will extend 140 miles downstream - from the town of Lewiston to its confluence with the Columbia River in south-central Washington State near the Tri-Cities.

READ PAST ISSUES OF THE HOT WATER REPORT

Data Sources: The 2025 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. There is no data available for the Lower Monumental 10-year average water temperature. Graphs and tables are assembled by SOS Staff.