Hot, Dry Summer Impacts Chehalis Basin Chinook Salmon


Dead and dying spring Chinook salmon were found in the Newaukum River basin this summer.

The root of the problem is in the historic Pacific Northwest heat wave experienced this summer and the ongoing drought.

The Chehalis River Watershed, which covers parts of Lewis, Thurston, Grays Harbor, and Mason County, did not have measurable rainfall of 85 days.

This surpasses the previous rainless streak of 55 days set in 1960. The Washington state Department of Ecology labeled March through May 2021 as the second driest on record since 1895.

The heat wave and lack of rain left many waters warmer than usual, and lowered water levels in many of our lakes and rivers.

What effect did this hot and dry summer have on our Chehalis River basin salmon?

According to Lea Ronne, a fish biologist with the Washington Department of Fish and Wildlife, who has been surveying streams in Lewis County’s Newaukum River this summer, “23 spring Chinook salmon were reported to have been killed, with heat as the greatest contributing factor. Water temperatures in parts of the basin were as high as 88 degrees Fahrenheit. Salmon are a cold-water species and begin to experience stress at 64.4 degrees Fahrenheit.”

Lea continued, “During warm weather, salmon depend on the water at the bottom layers of deeper pools to be colder than the rest of the water to provide ‘cold water refugia.’”

Refugia are areas where species can survive during adverse conditions.

“This summer many people also sought refuge from the heat and swam in the deeper Chehalis River and its tributaries pools. The swimming mixed up the layers of water, which resulted in the loss of bottom river layers of cold water.

“These human conflicts coincided with the movement of spring Chinook salmon and were the ‘straw that the broke the camel’s back’ as these spring Chinook had been in the freshwater river system a while, and more susceptible to stress and disease,” according to Lea.

What can be done in the future to protect salmon habitat while enhancing salmon resiliency?

The main way people can keep fish kills like this from happening again are to protect and help to create additional deep pools for salmon. You can help by:

• Using water wisely. The less water you use in your home and yard means more water left in rivers, streams, or as groundwater. Groundwater recharges our streams and rivers to maintain stream flows and provides cooler water temperatures.

• Protecting or planting native vegetation along our streams and rivers riparian corridors. Big trees and overhanging vegetation are essential in keeping the water in our streams and rivers cool.

• Leaving or placing large wood in the river. Large wood helps create habitat complexity and deeper pools of water with cold water salmon can take refuge in.

• If you observe any dead or dying fish in the summer, please report it on the state Department of Fish and Wildlife’s Environmental Fish/Shellfish Die-off Report form found at:

• After documenting or reporting the dead or dying fish, push fish downstream to release key fish nutrients in the river needed by wildlife and native plants. This also protects pets from potentially harmful contact with salmon carcasses.

Rain is in the immediate forecast, and we may get higher than normal levels of rain in the coming months, according to the Office of the State Climatologist.

For more information on how to protect salmon in your local rivers and streams, please contact Kirsten Harma, Chehalis Basin Lead Entity Coordinator at 360-488-3232 or email at Or contact Lea Ronne, Fish Biologist III, WDFW at

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