Sockeye salmon with lesions dying from hot water in the Columbia-Snake River Basin © Conrad Gowell
Welcome to the Hot Water Report 2024: Warming Waters in the Lower Snake and Columbia Rivers.

 I. EXECUTIVE SUMMARY

• All four lower Snake River reservoirs register temperatures above the 68°F “harm” threshold. Ice Harbor Dam reservoir was the warmest this week - at 72.28°F on July 23.
• The Idaho Department of Fish & Game (IDFG) reported on July 22 that significant numbers of Snake River sockeye have been observed seeking refuge from hot water in the lower Snake River by moving (straying) into the Mid-Columbia River, where temperatures are cooler.
• Scientific studies and computer models demonstrate that a free-flowing lower Snake River would absorb far less solar radiation compared to reservoirs with the dams in place. This would result in considerably cooler waters and deliver significant survival benefits to migrating juvenile and adult salmon and steelhead. Salmon can withstand some exposure to warm water. However, the longer the exposure and higher the temperatures, the greater the harms. Eliminating the four slack water reservoirs created by the lower Snake River dams would also shorten migratory travel time and energy expenditures, reduce overall exposure to hot water as well as harmful impacts from in-reservoir predation.

II. INTRODUCTION

Return 2021, acrylic painting on birch panel, 30" x 60 © Josh Udesen

The Columbia-Snake federal hydro-system harms and kills both juvenile and adult fish in multiple ways, including by elevating water temperatures in the summer months in their large, stagnant reservoirs. These cold-water fish begin to suffer harmful effects when water temperatures exceed 68°F.

All four lower Snake River reservoirs currently register temperatures above the 68°F “harm” threshold. Ice Harbor Dam reservoir registered the highest water temperature of 72.28°F on July 23. Lower Monumental Dam reservoir registered the second highest temperature at 71.53°F on July 24.

In this issue, we spotlight the emergency salmon transportation program recently begun by the Idaho Department of Fish and Game (IDFG) in an effort to protect critically endangered sockeye salmon from deadly hot water conditions in the lower Snake River reservoirs this summer. While this is an important project to improve this year’s returning adults’ survival by removing them from a lethal river, the science remains clear: protecting Snake River fish from extinction and rebuilding their populations to abundance in the long-term requires restoring a free-flowing lower Snake River.

During the summer, the Hot Water Report provides real-time water temperatures in the lower Snake and Columbia river reservoirs, with updates 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 the Hot Water Report issues at wildsalmon.org/HWR

III. 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.
• Data collection: 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. The water temperatures are taken on the hour. Hourly temperatures are used to find the highest temperatures reached in each reservoir, and hourly temperature measurements are used to find the daily average temperatures.
• Average Water Temperature Graphs (below): Daily average temperatures are represented with solid lines, and the 10-year average (2014 - 2023) temperatures are with dashed lines of the same color. The dotted line across the graph represents the 68°F “harm threshold” for adult and juvenile fish.
• Weekly High Water Temperature Tables (below): This table outlines the highest water temperatures reported for each reservoir during the week and how many days water temperatures have exceeded 68°F.
• Hot water temperature effects to salmon: The longer and the higher water temperatures rise above 68°F, the greater the harm to salmon, including: migration disruption, increased metabolism, increased susceptibility to disease, reduced reproductive potential (by reducing egg viability), suffocation (warm water carries less oxygen), and in worst case - death.

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

LOWER SNAKE RIVER WATER TEMPERATURES: 7/18 - 7/24

Lower Snake River - 2024 Daily Average and 10-year Average.

Lower Snake River Water Temperatures - 2024 Daily Average and 10-year Average. Click on the image to view the graph and click here to view the PDF version with separate graphs for each reservoir.

• Lower Snake River Average Water Temperatures: this week, the reservoir behind the Ice Harbor Dam experienced a high average water temperature of 71.76°F on July 24, exceeding its 10-year average of 70.90°F.
• The reservoir behind Lower Monumental Dam experienced an average temperature of 71.15°F on July 24. 
• Little Goose Dam reservoir saw an average water temperature of 70.16°F on July 21 and July 24.
• Lower Granite reservoir saw an average water temperature of 68.07°F, above its 10-year average of 66.80°F. This week, the Lower Granite Dam's reservoir’s average also registered below 67°F from 7/19 - 7/22 due to the US Army Corps of Engineers' cold water releases from the reservoir behind Dworshak Dam.

WEEKLY HIGH TEMPERATURES IN THE LOWER SNAKE RIVER: 7/18 - 7/24

• The Ice Harbor Dam reservoir registered the highest water temperature of 72.28°F on July 23.
• Lower Monumental Dam reservoir registered the second highest temperature of 71.53°F on July 24.
• The Little Goose Dam reservoir registered a high temperature of 71.29°F on July 24.
• Lower Granite Dam reached a high water temperature of 68.83°F on July 18.  

LOWER COLUMBIA RIVER WATER TEMPERATURES:  7/18 - 7/24

Lower Columbia River - 2024 Daily Average and 10-year Average.

Lower Columbia River Water Temperatures - 2024 Daily Average and 10-year Average. Click on the image to view the graph and click here to view the PDF version with separate graphs for each reservoir.

• This week, all four reservoirs on the lower Columbia River experienced average water temperatures above the 68°F “harm" threshold.
• The reservoir behind the Bonneville Dam, The Dalles Dam, and John Day Dam had a high average temperature of 71.42°F on July 21, exceeding its 10-year average temperature.
• The reservoir behind McNary Dam reached an average temperature of 69.58°F on July 24.

WEEKLY HIGH TEMPERATURES IN THE LOWER COLUMBIA RIVER: 7/18 - 7/24

• On the lower Columbia River, the John Day Dam reservoir registered the highest water temperature at 72.68°F on July 21.
• The Dalles Dam reservoir reached the second highest water temperature at 71.78°F on July 21.

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. Lower Monumental 10-year average water temperatures are unavailable. Graphs and tables are assembled by SOS Staff.

V. Removing dams will reduce lower Snake River water temperatures and deliver critical survival benefits to endangered salmon and steelhead

Water temperatures in the lower Snake River continue to rise between 68°F - 72°F, a range that causes significant harm to salmon, where they can experience reduced available oxygen; increase susceptibility to parasites, predators, and disease; alter growth and development rates for juvenile salmon; energy depletion, and a disruption in migration.

Map of the Mid-Columbia River and lower Snake RiverThe Idaho Fish & Game Department (IDFG) reported on July 22 that Snake River sockeye have been observed seeking refuge from hot water temperatures in the lower Snake River by moving (straying) into the Mid-Columbia River, where water temperatures are cooler. The Department reports, over the last two weeks, 15 PIT-tagged Snake River returning adult sockeye were observed at the Priest Rapids Dam on the mainstem Columbia River upstream from its confluence with the Snake River. Scientists estimate that approximately 16% of the total Snake River sockeye run detected earlier this year passing Bonneville Dam have ‘strayed’ into the Mid-Columbia River region because water temperatures there are cooler. To compare, on July 24, Priest Rapids forebay registered an average water temperature of 65.04°F, whereas Ice Harbor forebay average temperature is 71.76°F - a substantial difference of more than 6°F.

Emergency Sockeye Salmon Transportation

In early July, due to dangerous temperatures in the lower Snake River reservoirs, the IDFG began an emergency rescue effort for Snake River sockeye by capturing adults at Lower Granite Dam and trucking them to the Eagle Fish Hatchery near Boise, ID. Trucking salmon to a hatchery can be an effective immediate stop-gap measure to conserve sockeye salmon’s genetic information and prevent the extinction of this species, but it is not a viable long-term solution. IDFG staff will continue to truck Snake River sockeye salmon from Lower Granite Dam throughout July.

Breaching the lower Snake River dams will restore colder water to help migrating juvenile and adult salmon and dramatically improve their survival

IDFG undertook similar emergency salmon trucking efforts in 2015 and 2021 when weather and river conditions also turned deadly for migrating salmon. In the summer of 2015, at least 96 percent of returning Snake River sockeye salmon run died in the lower river because the reservoirs, coupled with record air temperature and low flows, elevated water temperatures to deadly levels. Snake River sockeye are among the most endangered in the Columbia Basin today. The effects of the federal hydro-system, in combination with the changing climate, are steadily elevating water temperatures in the lower Columbia and lower Snake rivers. Over time, these hot water episodes in summer are becoming more frequent, longer lasting, and more intense. Policymakers and Northwest dam and fish managers need to make big adjustments to the federal hydro-system and how we operate it in order to help struggling salmon and steelhead populations survive and begin to rebuild.

Scientific studies and computer models demonstrate that a free-flowing lower Snake River would have remained cool enough for salmon to migrate successfully despite the low snowpack and hot ambient temperatures that occurred in 2015.

Columbia Riverkeeper published a report: Computer modeling shows that Lower Snake River dams caused dangerously hot water for salmon in 2015—evaluating what the water temperatures of the lower Snake would have been during the summer of 2015 if its four federal dams did not exist. Through computer modeling, Columbia Riverkeeper found that each of the four reservoirs behind the dams increased the river temperature by about 2°F - 4°F (figure 1). The reservoirs create large, stagnant pools that steadily absorb heat from the sun. When warm water from one reservoir moves downstream to the next pool, the already-warmed water is stopped again by the next dam and continues to heat up. The model indicates clearly that this effect would be absent from the free-flowing lower Snake River.

Since Columbia Riverkeeper published its study in 2017, federal science agencies, U.S. Army Corps of Engineers¹ and EPA, released more information corroborating its findings. EPA released a study showing that, in warm years, water flowing into the lower Snake River is cool enough for fish, but water flowing out of the lower Snake River is too hot, and the dams are the main cause of this heat pollution.²

Cool water from Dworshak reservoir provides relief to migrating salmon

A free-flowing lower Snake River would not absorb the same amount of solar radiation and the resulting considerably cooler waters would deliver big survival benefits to migrating juvenile and adult salmon and steelhead populations. A free-flowing lower Snake River would also greatly expand the benefit of cold water released from Dworshak reservoir upstream on the Clearwater River in the hot summer months.

Dworshak Dam was completed in 1973. Its large reservoir is managed in summer months to release its very cold waters into the Clearwater River, just upstream from its confluence with the Snake River at Lewiston, Idaho. This week, for example, Dworshak reservoir average water temperatures are very cool, ranging between 42°F - 43°F. Dworshak’s cold water releases help keep the Lower Granite Dam reservoir (on the lower Snake River) cooler than it would otherwise be. However, as long as the four lower Snake River dams remain in place, the benefits of Dworshak’s cold flows into the lower Snake River are highly limited and serve only as a local, short-term solution to cooling water temperatures in this one reservoir. There are no detectable water temperature benefits to help struggling fish populations in the three downstream reservoirs.

By restoring this 140-mile stretch of the lower Snake River, models show that, while temperatures in a freely flowing river may spike above 68 degrees periodically, they will quickly return to the cool temperatures that salmon and steelhead need to survive and migrate. With a freely-flowing lower Snake River, cold water released from Dworshak Dam during the summer months would further help keep temperatures cool and healthy for fish from Lewiston (ID) downstream to where the Snake River joins the Columbia River in south-central Washington State near the Tri-Cities.

A restored lower Snake River would provide the largest availability of high-quality free-flowing, cold-water habitat for salmon populations to recover to significant levels of abundance, help salmon reach their spawning grounds. The benefits of dam removal would improve the ability of migrating fishes to access high-elevation, groundwater- and snowmelt-fed freshwater refuges, increasing survival and productivity in what will be increasingly challenging climate conditions.

References:
1. U.S. Army Corps of Engineers, Final Environmental Impact Statement for Columbia River System Operations, Appendix D, p. A-1-28 (2020).
2. EPA, Columbia and Lower Snake River Temperature TMDL, pp. 47–50 (2020).

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, Natural Resources Defense Council, 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