Climate Change and Salmon


Waters are Warmer Longer

Climate change is threatening the clean, cold, and plentiful water in rivers that salmon need to survive. The average annual air temperature across Washington increased by 1.77 degrees Fahrenheit between 1960 and 2020,9 a trend that is projected to continue but at an even faster rate as heat-trapping atmospheric carbon dioxide levels continue to climb.

Glaciers, which provide cold water to streams in the Pacific Northwest, are vanishing. In addition, mountain snowpacks are becoming smaller over time as average temperatures increase and freezing elevations rise. The amount of water in streams in the summer, when young salmon are at a critical life stage, has become lower in most streams,10 and for longer periods of time. Scientists estimate that the amount of water that was released from melted snow declined 21 percent in the western United States from 1955 to 2016.11 Compounding the low-flow problem, water is being removed from rivers to irrigate farmland and accommodate an increasing human population.

As summer low flows decline and the air warms, water temperatures in rivers increase. Water temperatures greater than 64 degrees Fahrenheit stress salmon, and temperatures above 70 degrees Fahrenheit can be lethal.12 Without actions to reduce water temperatures, there will be fewer salmon and fewer rivers where they can survive.

The changing climate also is bringing rain instead of snow to some areas. With more rain, winter stream flow will increase by 25-34 percent by the 2080s, increasing the likelihood of severe flooding in the winter.13 Severe flooding becomes catastrophic when floodplains, which are natural storage areas for flood water, are developed for commercial and residential use.

As peak flows change in volume and season, the life cycles of salmon are being disrupted. More intense floods can destroy redds (salmon nests), reduce habitat complexity, and flush young salmon out of their calm-water habitat, reducing their chance for survival. While some juveniles may survive this premature transition from freshwater to saltwater, many won’t be large enough to catch prey or avoid being eaten.14

a graphic containing mountains, map of Washington, river with fish and a treed hillside


More Data About Water

Water Quality


Stormwater running off impermeable surfaces is the top pollution source impacting Puget Sound.25 As cities and suburbs have expanded, impermeable surfaces such as pavement, roofs, and other hard surfaces have increased.

As rain runs off these surfaces, it collects pollution from oil, fertilizers, pesticides, vehicles, and animal manure before heading, usually untreated, into street drains and then directly into streams, bays, and the ocean. Untreated stormwater can decrease the oxygen levels in the water,26 limit the ability of some salmon species to find food and avoid predators, make fish more susceptible to disease, and kill large numbers of fish in urban streams.27

Ocean Conditions

Human activities have resulted in record-breaking levels of carbon dioxide in the atmosphere and in the oceans.15 Excess carbon dioxide is absorbed by the ocean, forming carbonic acid, which increased the average ocean acidity level by 30 percent since the Industrial Revolution.16

Increased acidity damages the phytoplankton, zooplankton, and crustaceans salmon eat. Excess carbon dioxide also can change the way salmon use their sense of smell to find food, avoid being eaten, and find their natal streams.17

The warmer climate also impacts ocean temperatures. The near-surface average water temperatures off Washington’s coast have been warming during the past 50 years.18 Warmer water has fewer nutrients and less oxygen than colder water and creates conditions less beneficial for salmon. For example, warmer water favors sub-tropical zooplankton, which are poor food for juvenile salmon and the fish they eat, making survival less likely.

Salmon have demonstrated during the past 10,000 years that they can adapt to a changing environment. However, climate change is speeding up these environmental changes, and when combined with fewer natural buffers, degraded habitats, and their lost genetic diversity, salmon struggle to adapt quickly enough, threatening their continued existence.

The climate crisis requires immediate action to reduce pollutants that are accelerating climate change and build climate resiliency for people and salmon. In 2021, Governor Jay Inslee signed the Climate Commitment Act into law, committing to reduce Washington’s greenhouse gas emissions by 95 percent by 2050.19

In addition, several grant programs are focusing on mitigating the increasing toll of climate change on watersheds. Salmon Recovery Funding Board grant applications require recipients to address climate resiliency and the innovative Floodplains by Design grant program supports floodplain reconnection and streambank protections, which can reduce the impacts of climate change. Without actions to reduce water temperatures, there will be fewer salmon and fewer rivers where they can survive.

Water Temperature Violations Across the State

The data in the chart below are collected by the Washington Department of Ecology from 187 stations across the state. These stations are used to record various water quality parameters including oxygen levels, bacteria concentration, and water temperature. Metrics collected at these stations are compared to set the standards to regulate water quality. Where the recorded temperature was above the set standard, it is considered a violation.

Looking at the number of violations a station has over time can provide insight into trends in water temperature. Using this data, in combination with other current research, scientists can see an increasing trend in the number of times water temperature was warm enough to exceed the standard. Across the state, there have been substantially more exceedances since 1997.

Frequency of Water Quality Temperature Violations Over Time:

Data Source: Washington Department of Ecology

Water Quality Index Scores

Cold, clean water is essential for salmon and steelhead. This water quality measurement looks at temperature, acidity, and levels of oxygen, bacteria, nutrients, and sediment. The overall quality of Washington’s waters, not considering toxics, has improved since 1994.

The water quality at 48 percent of long-term water quality monitoring sites is improving.

Declines were seen at only 4.6 percent of the monitoring sites while 47.4 percent show no significant trend from 1994-2017.

Statewide Data 5

Statewide Data 6

Routine freshwater monitoring data collected by the Washington State Department of Ecology’s River and Stream Monitoring Program are summarized by a technique called the “Water Quality Index.”  The index ranges from 1 (poor quality) to 100 (good quality).

The map shows water quality index scores for long-term stations with 5 or more years of monthly data and may include stations monitored by organizations other than the Department of Ecology.

All current long-term Ecology monitoring stations with at least 5 years of data are included. Most stations shown are near the mouths of major streams. These stations integrate upstream water quality and capture large, basin-scale trends. However, status and trends at these locations may not reflect status or trends in any particular subbasin.

Annual scores were determined by water year, which runs from October to September, beginning with Water Year 1994.

The index summary does not include non-standard elements like metals. For temperature, pH, oxygen, and fecal coliform bacteria, the index is based on criteria in Washington’s Water Quality Standards, Washington Administrative Code 173-201A. For nutrient and sediment measures where standards are not specific, results are based on expected conditions in a given region. Multiple constituents are combined and results aggregated over time to produce a single score for each station and each year.

Find out more about water quality: The Department of Ecology’s Water Quality Atlas is an interactive search and mapping tool that accesses Water Quality Assessment category results by geographic location, water quality standards by location, areas covered by Total Maximum Daily Loads, and permitted wastewater discharge outfalls.

The Department of Ecology’s Freshwater Information Network is an interactive, map-based tool to search for freshwater monitoring data and sites across the state and is the source behind the Water Quality Index data presented in this report.

Water Quantity

The data below shows whether the summer low-flow trends are increasing or decreasing over the long-term and the strength of the evidence.

Washington Streams: 60-Day Summer Low Flow Trends:

The advantage of a long-term data set is that the influence of annual weather differences and cyclic climate changes (e.g., el niño and la niña or the phases of the Pacific decadal oscillation) are minimized over time. Because trends are measured over decades, this indicator is not sensitive to relatively short-term changes occurring over just a few years even if significant flow restoration occurs. To measure a change in trend, either large changes in flow must occur (such as a dam setting minimum downstream flows) or a very consistent change over a long period of time is needed.

Note: The analysis for the chart above does not include data about regulated streams with dams. Also, some geographic areas of the state have very few evaluated streams. Therefore, results may greatly differ from other analyses and may not adequately reflect some individual regional trends.

Data Source: Washington Department of Ecology