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.

Climate change has warmed the air across Washington by 0.15 degree Fahrenheit every decade during the past 100 years,23 a trend that is projected to continue but at an even faster rate, reaching increases of up to 5.3 degrees Fahrenheit every decade by 2090.24

As the air warms, glaciers, which store much of the freshwater in the Pacific Northwest, melt and have less cold water to feed streams in the summer when salmon need it the most. Scientists already are seeing less water in summer streams,25 and for longer periods of time. Compounding the problem during low-flow periods is when more water is removed from rivers to irrigate farmland and accommodate demands of an increasing population. As the amount of cold water from glacier-fed rivers declines, the water temperature in rivers will continue to increase.

Graphic of 3 mountains with decreasing snowpack and 3 rivers with increasing temperatures


Streams with temperatures greater than 64 degrees Fahrenheit can stress salmon, and when rivers reach 70 degrees Fahrenheit, salmon begin to die.33

Challenges 10

The amount of snow in the mountains is decreasing. Scientists project that the average spring snowpack in Washington will decline by 56-70 percent by the 2080s.28 Some Washington streams are getting hotter, stressing salmon. Scientists estimate that 1,016 Puget Sound river miles will exceed 64 degrees Fahrenheit for up to 7.5 weeks.29

The changing climate also is bringing rain instead of snow to some areas. With more rain, scientists predict winter stream flow will increase by 25-34 percent by the 2080s,34 increasing the likelihood of severe flooding in the winter.35 This issue is compounded when floodplains, which are natural storage areas for excess water, are developed for other purposes.

Not only is the amount of water in streams predicted to change but so is the timing. Scientists already are seeing annual peak flows occurring 1 to 4 weeks earlier.36

As peak flows change in volume and season, the delicate life cycle of salmon may be disrupted. Glaciers and snowpack are melting earlier in the season. Faster and stronger running rivers can destroy redds (salmon nests) and flush young salmon out of their calm-water habitat, reducing their chance for survival.37 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.38


More Data About Water

Water Quality


Stormwater running off paved and hard surfaces is the top pollution source impacting water bodies in and around Puget Sound.17

As rain runs off impervious surfaces such as roofs, roads, and pavement, it collects pollution from oil, fertilizers, pesticides, garbage, and animal manure before heading, usually untreated, into street drains and then directly into streams and bays and then the ocean.18

This soup of toxins in untreated stormwater can decrease the oxygen levels in the water,19 limit the ability of some salmon species to find food and avoid predators, and sometimes lead to large fish die-offs in urban streams.20

As Washington’s population continues to grow, threats to water quality are likely to increase, creating more challenges for salmon recovery.

Ocean Conditions

Human activities have resulted in record-breaking levels of carbon dioxide in the atmosphere and in the oceans.39 Excess carbon dioxide is absorbed by the ocean, forming carbonic acid, which has driven up the average ocean acidity level by 30 percent since the Industrial Revolution.40 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.41

The climate also impacts ocean temperatures. During the past 50 years, the near-surface waters off Washington’s coast have warmed by roughly 1.8 degrees Fahrenheit.42 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.

The National Oceanic and Atmospheric Administration monitors changes in the ocean and reports how they may affect young salmon.

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