Sockeye salmon with lesions dying from hot water in the Columbia-Snake River Basin ©Conrad GowellWelcome to the Hot Water Report: Warming Waters in the Lower Snake and Columbia Rivers. 

I. EXECUTIVE SUMMARY

• For decades, summer water temperatures in the lower Snake and Columbia rivers have been rising to levels that are lethal to salmon and steelhead, due to the presence of dams and their hot, stagnant reservoirs. 
• All four Snake River salmon and steelhead populations are listed as threatened or endangered. Populations declined precipitously shortly after the dams were constructed. 
• On August 2023, Ice Harbor Dam’s reservoir reached 72.73°F —more than 4 degrees above the 68°F “harm” threshold, the legal and biological limit identified to protect salmon.
• Extreme heat warnings are becoming more frequent across the country this year. In particular, the Northwest is expected to experience above-average high temperatures, continued drought emergencies, and low river flow conditions—all of which threaten to increase river temperatures to harmful levels.  
• Scientists have reached a conclusive answer: Restoring the lower Snake River by breaching the four dams is the only action available to provide cooler water temperatures and protect salmon and steelhead from extinction.

II. INTRODUCTION

Salmon Columbia River © Dave McCoy

For millennia, wild Snake and Columbia River salmon and steelhead have delivered vast cultural, economic, nutritional, and ecological benefits to the people, fish, and wildlife of the Northwest. Before the lower Snake River dams were built, the pristine, clear, cold waters of the Snake River Basin were home to millions of adult salmon and steelhead. Each year, they return from the Pacific Ocean, swimming against the current in search of their natal spawning gravels and delivering many millions of pounds of high-quality marine-derived nutrients to the landscape and wildlife of the Northwest. And even as they dwindle toward extinction, their resilient nature continues in a fight for the species’ survival.

Today, however, the dams and reservoirs have stilled the current, and salmon now require a month or more to reach the ocean, migrating in warm water reaching over 68°F the biological and legal threshold scientists identified to protect salmon. All four Snake River salmon and steelhead populations are listed as threatened or endangered under the Endangered Species Act and are at grave risk of extinction.

Restoring a free-flowing Snake River by removing its four lower dams and replacing their services is essential to provide cold, clean, healthy water for salmon and steelhead; protect and recover these once-highly prolific fish populations; uphold our nation's promises to Tribes; and help feed the critically endangered Southern Resident orcas and other fish and wildlife species.

During the summer, the Hot Water Report will provide an update on real-time water temperatures in the lower Snake and Columbia river reservoirs and reports from scientists, Tribal members, fishing guides, and other experts about the challenges facing these rivers, our opportunities to recover healthy, resilient fish populations, and the benefits they deliver to Northwest communities and other fish and wildlife populations.

View previous Hot Water Report issues at wildsalmon.org/HWR

III. Restoring a healthy lower Snake River for 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

In 2023, salmon and steelhead experienced another summer of hot, harmful water temperatures in the lower Snake River. From early July to September, all four lower Snake River reservoirs had water temperatures above 68°F, many of the reservoirs reaching over 62 days above 68°F. On August 2023, the reservoir behind the Ice Harbor Dam registered the highest temperature recorded during the summer at 72.73°F – more than 4 degrees above the 68°F “harm” threshold.

This year, warnings of extreme heat are becoming more frequent across the country and in the Northwest. The NW is expected to see above-average high temperatures, continued drought emergencies, and low river flow conditions, all of which signal that river water temperatures will increase to harmful levels.

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.¹ Many of the Columbia-Snake River Basin salmon runs have been locally extirpated. Thirteen populations, including all four Snake River populations, are listed as threatened or endangered under the Endangered Species Act and remain at risk of extinction. In recent decades, adult salmon and steelhead migrating upriver to spawning grounds in the Columbia Basin have suffered decreased survival, largely in part due to the dangerously warm water in the Snake and Columbia Rivers, caused by dams that created slack water reservoirs.

Salmon Ecology:

Scaffold fishing at Celilo, Joe Palmer fishing from a hanging scaffold on Standing Island. Aug 1952. © Columbia River Inter-Tribal Fish Commission/Raymond Mathen

“The percentage of natural-origin salmon and steelhead returning to spawn today compared to historic levels is even smaller; wild-origin returns of salmon to the Snake Basin are 0.1-2% of their historical abundance, with many populations at or below a quasi-extinction threshold. Because of the severe lack of fish, the Basin Tribes cannot exercise their harvest rights to the same extent they could at the time the rights were reserved in treaties or in executive orders.” – Tribal Circumstances Analysis, prepared by Department of Interior in collaboration and coordination with the Columbia Basin Tribes

Since time immemorial, salmon have been integral and profoundly fundamental to Northwest Tribes’ spiritual and cultural identity, economic prosperity, and sovereignty.² Salmon and steelhead are a critical nutrient link between oceans, rivers, streams, forests, and wildlife. Salmon runs function as enormous pumps that provide vast amounts of marine nutrients from the ocean to river systems.³ Over 137 species benefit from and utilize the ocean-origin nutrients that salmon and steelhead deliver.⁴ Because of their vast ecological impact, salmon are considered a keystone, connector, and indicator species. In other words, salmon have unique and substantial effects on their own and neighboring environments such that no other species can replace its particular ecological role. When keystone species are removed, the entire ecosystem typically collapses.

The state of salmon populations reflects the overall health of the ecosystem as a whole. When salmon populations are in peril, it indicates that the entire ecosystem is unhealthy and/or under stress.

The lower Snake River dams' impact on freshwater habitat and salmon:

Salmon and steelhead require clean, cold water, intact and contiguous rivers, and reliable streamflows for spawning, rearing, and migration. Prior to the construction of the four dams on the lower Snake River, the pristine, clear, cold waters of the Snake River Basin were home to millions of adult salmon and steelhead.⁵ When the Columbia-Snake rivers flowed freely, juvenile salmon and steelhead took as few as five days to complete their migration to the ocean– due to the swiftly moving current of the Snake and Columbia rivers. Today, however, the dams and reservoirs have stilled the current, and salmon now require a month or more to reach the ocean.

Now, endangered Snake River salmon and steelhead must traverse through four dams on the lower Columbia River and four dams on the lower Snake River on their migration to the ocean and again on their journey back upstream as adults.

“Scientific studies continue to show that breaching the four lower Snake River dams would provide greater certainty of achieving long-term survival and recovery of native wild fishes more than any other measure or combination of measures without dam breaching.” – The American Fisheries Society (AFS) and The Western Division AFS

The lower Snake River dams create stagnant reservoirs, which are large, slow-moving pools which absorb enormous amounts of solar radiation, causing water temperature to reach lethally high levels. The reservoirs warm during the summer months and create a block of slow-moving hot water that retains the heat through the night and does not cool only until air temperatures drop. These warming waters inundate and destroy diverse micro-habitats that healthy rivers support, including cold-water refuges that salmon and steelhead rely upon during summer migrations. Without these vital pockets of cold water, salmonids cannot rest and recover on their journeys – adults moving upstream to spawn and juveniles moving downstream to the ocean.

Warming waters in the lower Snake and Columbia Rivers:

Sockeye salmon dies after record high temperatures in the Columbia River. © Conrad Gowell/Columbia Riverkeeper

The reservoirs on the lower Snake River increasingly warm the river above critical levels from July to mid-September, significantly reducing salmon reproduction and survival. Excessively high water temperatures, above 20°C/68°F (this threshold is the legal and biological limit scientists identified to protect salmon), are now normal for extended periods in July, August, and September.⁶

Rising temperatures and reductions in snowpack in recent decades due to climate change have resulted in warmer waters, which results in lower survival and reduced reproductive success for salmon and steelhead. The lower Snake River dams exacerbate these already warmed waters, creating conditions that harm these fish. Studies have also indicated that all Snake River salmon species (sockeye, spring/summer Chinook, fall Chinook, and steelhead) experience reduced survival at elevated water temperatures above 64°F, depending on the timing of their upriver migration.⁷ Steelhead, fall Chinook, and sockeye have greater exposure to high temperatures because they migrate in the summer when temperatures are hottest. When water temperatures rise above 68°F, the longer the time they remain above that threshold, the greater the harm, including migration disruption, increased metabolism, increased susceptibility to disease, reduced reproductive potential (by reducing egg viability), suffocation (warm water carries less dissolved oxygen), and in the worst case - death.

“Cold-water resources to protect migrating salmonids in the existing hydrosystem are extremely limited; there are no additional resources available that can significantly cool the river. Restoring the lower Snake River by removing its four federal dams will significantly reduce mainstem water temperatures on a long-term basis, and is likely the only action that can do so, substantially lowering the risk of extinction for salmon and steelhead.” –  Letter to NW policymakers signed by 55 Fisheries and natural resource scientists 

Due to the elevated water temperatures in the stagnant reservoirs and other harm caused by the lower Snake River dams, salmon runs have been in steep decline for several decades. The decline of once-abundant salmon, steelhead, and other species in the Columbia River Basin has severely and inequitably impacted Tribes’ spiritual, cultural, physical, and economic health.⁸ Without immediate and meaningful conservation actions to reconnect the Northwest’s most emblematic fish to over 5,500 miles of pristine, cold-water river and streams in Idaho, Oregon, and Washington, Snake River salmon and steelhead populations will continue to decline toward extinction. Restoring a free-flowing Snake River by removing its four dams and replacing their services is essential to provide cold, clean, healthy water for salmon and steelhead, recover and protect these once-highly prolific fish populations from extinction, uphold our nation's promises to Tribes, and help feed critically endangered Southern Resident orcas.

References:
1. 8. Tribal Circumstances Analysis developed by the Department of Interior, in collaboration and coordination with the Columbia Basin Tribes.
2. Columbia River Inter-Tribal Fish Commission: Columbia River Fish Species.
3. Wild Salmon Center: Why protect Salmon.
4. The National Wildlife Federation: Chinook Salmon.
5. Columbia River Inter-Tribal Fish Commission: Tribal Salmon Culture.
6. 7. Letter to NW policymakers signed by 55 Fisheries and natural resource scientists.

IV. READING THE DATA - LOWER SNAKE AND COLUMBIA RIVER TEMPERATURES

Introduction to the water temperature data:

• Throughout this summer, the Hot Water Report will provide, on a weekly basis, an update on real-time water temperatures in the lower Snake and Columbia River reservoirs.
• The daily average and high water temperature data at the four reservoir forebays are measured with sensors stationed at various depths below the reservoir surface, immediately upstream from the dams in the lower Snake River and the lower Columbia River for 2024.
• Daily average temperatures are represented with solid lines and the 10-year average (2014 - 2023) temperatures with dashed lines of the same color.
• The dotted line across the graph represents the 68°F “harm threshold” for adult and juvenile fish.

V. DISCUSSION OF DATA - LOWER SNAKE AND COLUMBIA RIVER TEMPERATURES

AVERAGE LOWER SNAKE AND COLUMBIA RIVER TEMPERATURES 6/19 - 6/25:

Figure 1. Lower Snake River Water Temperatures - 2024 Daily Average and 10-year Average. Click on the image to view the graph.

Figure 2. Lower Columbia River Water Temperatures - 2024 Daily Average and 10-year Average. Click on the image to view the graph.

Discussion of average water temperature data:

• Since April, temperatures in the lower Snake River and the lower Columbia River reservoirs have steadily increased.
• Figure 1. Lower Snake River Water Temperatures: this week, the reservoir behind the Ice Harbor Dam reached a high average water temperature of 64.26°F on June 24 - June 25.
• Figure 2. Lower Columbia River Water Temperatures: this week, the reservoir behind the Bonneville dam had a high average temperature of 63.32°F on June 24 - June 25.
• Most water temperatures in the lower Snake River and lower Columbia River have reached at or above their 10-year averages. As we near the end of June, the water temperatures are below the 68°F “harm” threshold, which is good news for cold-water species like salmon and steelhead. However, we expect these temperatures will rise considerably in these reservoirs as the summer progresses.

WEEKLY HIGH TEMPERATURES IN THE LOWER SNAKE AND COLUMBIA RIVER: 6/19 - 6/25

• On the lower Snake River, the reservoir behind the Ice Harbor Dam registered the highest water temperature of 64.72°F.

• On the lower Columbia River, the McNary reservoir registered the highest water temperature at 64.53°F.

Data Sources: The 2024 lower Snake River and lower Columbia River water temperature data presented in the Hot Water Report are collected from the USGS, Columbia River DART program by Columbia Basin Research, University of Washington, using data courtesy of the U.S. Army Corps of Engineers (USACE). 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.

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

View previous Hot Water Report issues at wildsalmon.org/HWR