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 water on 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 salmon face, and the opportunities to heal the river and the ecosystem.
EXECUTIVE SUMMARY:
- The Hot Water Report: Issue 1 dives into how the lower Snake River dams have transformed a healthy and free-flowing river into a series of large, warm, stagnant, toxic reservoirs that harm salmon and steelhead and severely impact their migration, reproductive success, and habitat quality.
- Hot water temperatures in the lower Snake and Columbia River: Each summer, water temperatures routinely reach lethal levels between 70-72°F, significantly above the 68°F legal and biological harm threshold for salmon and steelhead.
- The dams and reservoirs create an unhealthy and unnatural ecosystem: The lower Snake River dams transformed a healthy and free-flowing river into a series of large, warm, stagnant reservoirs—creating an unhealthy and unnatural ecosystem by restricting access to clean, cold, free-flowing water, promoting the development of toxic algal blooms, and adding pollutants when dams spill cancer-causing oil.
- Emergency procedures to protect salmon and steelhead from extinction: Columbia-Snake River fish populations, such as the Snake River sockeye and the Tucannon River spring Chinook, require emergency action, including emergency trapping and hauling to complete their life cycle, and strategies to preserve their genetic diversity.
- Path to recovery: The collaborative implementation of the CBRI represents our region’s greatest opportunity to achieve a healthy, resilient Columbia-Snake River Basin, uphold our nation's promises to Tribes, and reconnect endangered fish to 5,500 miles of pristine, protected rivers and streams in Idaho, Oregon, and Washington.
- Current lower Snake and Columbia River water temperatures: The reservoir behind the Ice Harbor Dam registered the highest water temperature of 68.79°F on July 4. The Dalles reservoir registered the highest water temperature at 69.26°F on July 8. Read more on water temperatures in the lower Snake and Columbia rivers here.
Warming waters in the lower Snake and Columbia Rivers
Since time immemorial, wild salmon and steelhead from the Snake and Columbia rivers have delivered vast cultural, economic, nutritional, and ecological benefits to the people, fish, and wildlife of the Northwest. Before the construction of the lower Snake River dams, the pristine, clear, cold waters of the Snake River Basin supported millions of spawning adult salmon and steelhead.
Today, salmon and steelhead face dramatically decreased survival rates, largely due to the federal system of dams and reservoirs in the Columbia River Basin. The dams on the lower Snake River in southeast Washington State—Ice Harbor, Lower Monumental, Little Goose, and Lower Granite—and their stagnant reservoirs heat up this historic, once highly productive river, harming and killing both juvenile and adult fish.
Wild salmon returning to the Snake River Basin are 0.1-2% of the abundance at the time the United States entered the 1855 Treaties with Tribes, which secure the right to fish at all usual and accustomed places.1 Many Columbia-Snake River Basin salmon runs have been locally extirpated. Today, Snake River salmon and steelhead return annually far below the recovery goals necessary to remove them from the protections of the Endangered Species Act and region-wide goals to achieve healthy and abundant populations.
Crisis on the lower Snake River
Below are the key impacts of hot water caused by the dams and stagnant reservoirs.
Dams and their reservoirs warm the river: The lower Snake and Columbia River dams create 140 miles of stagnant reservoirs, which are large, slow-moving, shallow pools that absorb enormous amounts of solar energy (heat), causing water temperatures to reach harmful levels for migrating salmon and steelhead during the summer months. Water moves slowly through these reservoirs, which gives water more time to accumulate heat and allows reservoirs to retain warm water throughout the day and night.2, 3 Water temperatures in reservoirs do not cool until air temperatures drop, typically in September. In comparison, a free-flowing river cools down much more quickly as air temperatures drop.4,5 Each summer in the lower Snake region, extreme heat warnings, droughts, reduced snowpack, and low river flow conditions all contribute to rising river water temperatures, which are then exacerbated by the dams and their reservoirs to harmful levels for cold water fish.
Impact of warm water on salmon and steelhead: Salmon and steelhead begin to suffer harmful effects when water temperatures exceed 68°F. Scientists have identified the 68°F threshold as the biological and legal water temperature limit under the Clean Water Act. In order to protect salmon and steelhead, water temperatures should remain at or under this threshold. During the summer, water temperatures in the lower Snake and Columbia River routinely reach lethal levels between 70-72°F. The longer and the higher water temperatures rise above 68°F, the greater the harm to the fish, including: migration disruption, increased metabolism, increased susceptibility to disease, reduced reproductive potential (by reducing egg viability), suffocation (warm water carries less oxygen), and in the worst case - death.
Hot water in fish ladders: Fish ladders are the only route for returning adult salmon and steelhead to pass the eight dams in the Columbia and Snake rivers. Fish ladders frequently contain warm surface waters that are hotter than the average river temperature, and such conditions create and/or exacerbate migration blockages.6,7,8 These blockages prevent successful migration to spawning grounds and attract predators, thereby reducing the survival and reproduction of salmon.
Warming waters destroy salmon and steelhead habitat and reduce their food availability: The reservoirs and the 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 journey. A cool, free-flowing lower Snake River can provide critical refuge for salmon and steelhead that survive the first part of their difficult journey, rather than forcing these fish to migrate through 140 miles of warm stagnant reservoirs and fish ladders. The warm waters in the reservoirs also impact the aquatic insects that salmon prefer to eat, as many of the insects are unable to survive at elevated water temperatures.9
Dams, reservoirs, and fish ladders lengthen salmon and steelhead’s migration journey: In a free-flowing river, juvenile salmon and steelhead migrating to the Pacific Ocean are carried by the river’s current. They return as adults, swimming against the current in search of their natal spawning gravels. But now, the eight dams, reservoirs, and fish ladders force salmon to use more energy to complete their journey and take more time to reach the ocean (juveniles) or spawning grounds (adults). In a healthy, free-flowing river, juvenile salmon used to take just 2–4 days to migrate from Lewiston to the ocean, but now, it takes them much longer, 10–30 days to complete their journey.
NOAA states in their "Rebuilding Interior Columbia Basin Salmon and Steelhead" report, restoring the lower Snake River via dam removal must be a centerpiece action to address the “hydrosystem threat by decreasing travel time for water and juvenile fish, reducing powerhouse encounters, 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.”
Emergency trapping and hauling: Today, Snake River sockeye, in particular, remain dependent on a life-support hatchery and need additional support to complete their life cycle and successfully reach their spawning grounds in Idaho. In 2024, returning adult Snake River sockeye changed their migration route (also known as straying) away from the warming waters in the lower Snake River and into cooler upstream waters of the Columbia River past its confluence with the Snake River. To help boost the survival of sockeye, the Idaho Department of Fish and Game initiated an emergency "Trap and Haul” operation at Lower Granite Dam, then transported salmon to the Eagle Fish Hatchery for artificial reproduction intervention. Trucking salmon to a hatchery can be an effective immediate stop-gap measure to conserve genetic information and prevent the extinction of this species, but it is not a viable long-term solution.
Extreme action is underway to save spring Chinook from the Tucannon River, a tributary of the Snake River: Salmon Managers Begin Safety-Net Strategy for Tucannon Spring Chinook (Newsdata)
Attempts to cool the river: Each summer, the US Army Corps of Engineers seeks to mitigate the hot waters created by the lower Snake River reservoirs by releasing cold water stored behind the Dworshak Reservoir. These cold waters flowing into the Clearwater River (a tributary to the lower Snake River) can lower water temperatures and aid salmon migration in the lower Snake River. Unfortunately, the benefits of this cold water infusion are extremely limited. The large, stagnant reservoir behind Lower Granite Dam near Lewiston prevents this cold water from entering and cooling the waters in the three downstream reservoirs. With a free-flowing lower Snake River, the great benefit of these cold water releases from the Dworshak reservoir will extend down the lower Snake River all the way to its confluence with the Columbia River.
The lower Snake River dams transformed a healthy and free-flowing river into a series of large, warm, stagnant reservoirs—creating an unhealthy and unnatural ecosystem by restricting access to clean, cold, free-flowing water, promoting the development of toxic algal blooms, and adding pollutants when dams spill cancer-causing oil.
Toxic algal blooms: The warm and stagnant water conditions created by the dams allow toxic algal blooms to grow and make the river sick, unsafe, and dangerous for people, pets, communities, the environment, and already-endangered salmon and steelhead. These toxic algal blooms are also straining the limited recreational and fishing opportunities on the lower Snake River.
In the summer of 2023 and 2024, Whitman County Public Health Department confirmed large toxic algal blooms in the lower Snake River. The 2024 toxic algal bloom stretched intermittently between all four lower Snake River dams.
Oil spills: The lower Snake River dams spill oil and lubricants into the river. The oils used cause cancer and other adverse health effects in people. In 2012, the Army Corps reported discharging over 1,500 gallons of PCB-laden transformer oil at the Ice Harbor Dam, which exceeded the state and federal chronic water quality standards. In 2017, Lower Monumental Dam spilled over 1,600 gallons of oil into the Snake River, and in 2022, Little Goose Dam spilled oil into the Snake River for over 90 days.
Hot water is a pollutant: The Clean Water Act defines heat as a pollutant. The states of Oregon and Washington recognize that the lower Columbia and Snake rivers have too much heat pollution (warm water) to safely support salmon and steelhead. The dams are identified as a key source of heat pollution in the Columbia and Snake rivers.
Dams wasting water through evaporation: The lower Snake River dams waste approximately 30,400 acre-feet of water every year, due to evaporation from the reservoirs. The Stockholm Environment Institute’s study showed the water lost to evaporation each year could meet the residential needs of over 240,000 Washingtonians or grow over 8,000 acres of Washington apples.
Salmon and steelhead declines impact on the ecosystem: Salmon and steelhead are considered a keystone, connector, and indicator species. They are a critical nutrient link between oceans, rivers, streams, forests, and wildlife, with over 137 species benefiting from nutrients that salmon and steelhead deliver.10,11 However, the declines in salmon and steelhead populations have dramatically reduced the amount of species that feed on salmon, including the endangered Southern Resident orcas, as well as the loss of vital nutrients transferred annually from the ocean to freshwater ecosystems and their surrounding riparian habitats.12 The state of salmon populations reflects the overall health of the ecosystem as a whole, and when salmon populations are in peril, it indicates that the entire ecosystem is unhealthy and/or under stress.
Predators increase in warm waters: Warm, stagnant reservoir water creates an excellent environment for predator fish. Populations of native and invasive fish that eat salmon and steelhead have grown dramatically since the dams were constructed.13,14,15 Warm water accelerates these predators’ metabolism, which increases their ability to prey upon juvenile salmon and steelhead.16 With the elevated water temperatures, juvenile salmon are not able to swim as fast, which lengthens their travel time through all eight dams and reservoirs, leading to longer exposure to predation by piscivorous fish, native (pikeminnow) and non-native (small-mouth bass, walleye).
The path to recover salmon and steelhead
Red lesions and white fungus on the salmons’ bodies are the result of high water temperatures and stress. ©Conrad Gowell/Columbia Riverkeeper
Due to the elevated water temperatures in the stagnant reservoirs and other harms caused by the lower Snake River dams, salmon, steelhead, and other species in the Columbia River Basin have been in steep decline for several decades, inflicting severe consequences on the region’s ecosystem, wildlife, and communities. Of particular significance, the dams and reservoirs inequitably impact Tribal Nations’ way of life, violating treaty rights to fish and Tribes’ access to historic fishing grounds.
With this continuing crisis in the lower Snake River, and many Columbia-Snake River salmon and steelhead populations facing extinction, the “Six Sovereigns” — Confederated Tribes of the Umatilla Indian Reservation, Confederated Tribes of the Warm Springs Reservation of Oregon, the Confederated Tribes and Bands of the Yakama Nation, Nez Perce Tribe, State of Oregon, and State of Washington — jointly developed in 2023 the Columbia Basin Restoration Initiative (CBRI). It is a comprehensive, science-based, and durable strategy to restore salmon and other native fish populations to healthy and abundant levels, ensure a clean energy future, support local and regional economic and climate resilience, restore ecosystem function, and honor longstanding unmet commitments to Tribal Nations.
The collaborative implementation of the CBRI represents our region’s very best opportunity to date to achieve a healthy, resilient Columbia-Snake River Basin, uphold our nation's promises to Tribes, and reconnect endangered fish to 5,500 miles of pristine, protected rivers and streams in Idaho, Oregon, and Washington.
Stay tuned for the Hot Water Report: Issue 2 as we dive deeper into the CBRI and comprehensive solutions to recover the Columbia-Snake River salmon while also investing in our communities.
READING THE DATA: LOWER SNAKE AND COLUMBIA RIVER TEMPERATURES:
Introduction to the water temperature data:
- Throughout the summer, the Hot Water Report will provide 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 overall high water temperature levels that salmon and steelhead must migrate through to reach their spawning ground (adults) or to the ocean (juveniles).
- 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.
DISCUSSION OF DATA:
LOWER SNAKE RIVER WATER TEMPERATURES: 7/1 - 7/8
Average water temperature: This week, the reservoir behind the Ice Harbor Dam reached a high average water temperature of 68.45°F on July 5.
Highest water temperature: The Ice Harbor reservoir registered the highest water temperature of 68.79°F on July 4.
LOWER COLUMBIA RIVER WATER TEMPERATURES: 7/1 - 7/8
Average water temperature: This week, the John Day reservoir had a high average temperature of 68.36°F on July 7.
Highest Water Temperatures: The Dalles reservoir registered the highest water temperature at 69.26°F on July 8.
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.
References:
1. Tribal Circumstances Analysis developed by the Department of Interior, in collaboration and coordination with the Columbia Basin Tribes.
2,4, 6. Columbia Riverkeeper White Paper: Computer modeling shows that Lower Snake River dams caused dangerously hot water for salmon in 2015.
3. U.S. Environmental Protection Agency, Application of a 1-D Heat Budget Model to the Columbia River System, p.1 (2001) (“Construction of impoundments for hydroelectric facilities and navigational locks . . . increase the time waters of the Columbia and Snake are exposed to high summer temperatures . . . .”).
5. U.S. Environmental Protection Agency, Columbia River Preliminary Draft Temperature TMDL, p.26 (2003)
7. National Marine Fisheries Service, Endangered Species Act Section 7(a)(2) Consultation Regarding 1994–1998 Operation of the Federal Columbia River Power System and Juvenile Transportation Program in 1994–1998, p.76 (1994) (directing action agencies to address high water temperatures in fish ladders).
8. Keefer M.L. and C.C. Caudill. 2015. Estimating thermal exposure of adult summer steelhead and fall Chinook salmon migrating in a warm impounded river. Ecology of Freshwater Fish. https://doi.org 10.1111/eff.12238
9, 16. Washington State Department of Ecology: Effects of Elevated Water Temperatures on Salmonids
10. Columbia Basin Partnership Task Force 2020. A Vision for Salmon and Steelhead: Southern Resident Killer Whales and Ecological Perspective pg. 92
11. Cederholm, C. J., D. H. Johnson, R. E. Bilby, L. G. Dominguez, A. M. Garrett, W. H. Graeber, E. L. Greda, M. D. Kunze, B. G. Marcot, J. F. Palmisano, R. W. Plotnikoff, W. G. Pearcy, C. A. Simenstad, and P. C. Trotter. 2000. Pacific Salmon and Wildlife–Ecological Contexts, Relationships, and Implications for Management. Special Edition Technical Report, Prepared for D. H. Johnson and T. A. O’Neil, Wildlife-Habitat Relationships in Oregon and Washington. Washington Department of Fish and Wildlife, Olympia, Washington.
12. Orca Network: Selective Foraging and Sharing by Resident
13. Northwest Power and Conservation Council: Predation
14. Washington Department of Fish & Wildlife: Chinook Salmon (Snake River Spring/Summer ESU)
15. Columbia Basin Partnership Task Force 2020. A Vision for Salmon and Steelhead: Southern Resident Killer Whales and Ecological Perspective pg. 71
