The importance of cold water refuges to Pacific salmon and steelhead migrating through the Columbia River Basin recently has been well documented. Summertime water temperatures in the mainstem Columbia River have steadily increased over the last few decades, as has the length of these warm periods. Annual peak temperatures routinely exceed 21°C in most years and have been as high as 24°C. The warmest period typically occurs in July to early September, coincident with late-migrating summer Chinook and sockeye salmon and substantial portions of the fall Chinook salmon and summer steelhead runs. Water temperatures in the 19-22°C range are a significant concern because these temperatures can cause behavioral changes and a variety of sub-lethal effects on physiology, disease susceptibility, reproduction, and survival.
The information is carefully vetted with regional experts, at forums including the Estuary Partnership Science Work Group, the Columbia River Estuary Conference, and others, and results are widely disseminated so others can use the results in habitat restoration design or species recovery planning. If interested in learning more, please contact the Estuary Partnership.