Coho salmon don’t like high water temperatures.

“Warm water can be directly lethal to salmon,” said Sarah Zaniewski, salmon biologist for the Squaxin Island Tribe. “Even if they don’t die immediately, salmon certainly become less fit and are more likely to die before they reach adulthood.”

The tribe conducted a series of snorkel surveys throughout Skookum Creek in late summer and early fall looking for locations where juvenile coho could be found. Skookum Creek is an important coho producer in deep South Sound.

A few years ago the tribe used Forward Looking Infrared Radar (FLIR) to map stream temperatures throughout the Skookum watershed. FLIR technology allows researchers to map every square foot of surface water. The tribe found several locations where cooler water could provide refuge to salmon.

During this year’s snorkel surveys, the tribe found coho living in each one of those refuges. “No matter how good the habitat was otherwise, if the water was too warm, the fish wouldn’t be there,” said Zaniewski.

Much of Skookum Creek flows through active agricultural land, which means that many of the streamside trees that had shaded the creek historically aren’t there anymore.

Low flows spike temperatures during warm summer months. Like many South Sound streams, Skookum Creek is considered impaired by state and federal standards because of high temperatures.

The tribe and its partners have conducted a series of habitat restoration projects throughout the creek’s watershed, including adding large woody debris and supplementing gravel. Still, low flows leading to higher temperatures are a longterm problem in deep South Sound.

The treaty tribes aggregated stream gauge data in the recently released State of Our Watersheds Report. That report suggests that many South Sound streams failed to meet statutory minimum flows year-round since at least the 1980s.

One reason for lower flows and higher temperatures is the proliferation of permit-exempt wells. State law allows new wells to withdraw groundwater up to 5,000 gallons a day without obtaining a permit as proof that the water is legally available. “Every year, a dozen or so of these new wells come online in the South Sound,” Zaniewski said.

Now, with streams in the tribe’s treaty-reserved fishing area facing the impacts of climate change, cold water refuges will become increasingly important. “Climate change for salmon is going to be big deal,” Zaniewski said. “The more we can do to protect salmon by shading the streams and allowing higher consistent flows, the less we need to worry about climate change.”