Water Temps Extremely Stressful for Most Salmonid

On June 10, 2024, at 5:45 PM PDT, the recorded temperature was 72.50 degrees Fahrenheit. This data is provisional and may be subject to further verification. A similar observation was made on June 7, 2024, at 8:45 PM PDT, where the temperature was recorded at 72.32 degrees Fahrenheit, fluctuating between 66º and almost 74º for the first weeks in June.

The ideal water temperature range for salmonids (salmon, trout, etc.) in rivers and streams is generally between 55-64°F (12.8-17.8°C).[1][2][3] This optimal range allows them to thrive and complete their life cycles without stress.

However, as water temperatures increase beyond this ideal range, salmonids begin experiencing negative impacts:

Critical Warm Temperatures

• Around 68°F (20°C): Adult salmon have difficulty migrating upstream and become sluggish.[3] Juvenile growth and development rates can be altered.[3]
• 70°F (21.1°C) and above: Extremely stressful for most salmonid species.[3] Migration can stop altogether at 72-73°F (22.2-22.8°C).[3]
• 77°F (25°C) and above: If exposed for over 24 hours, salmonids will likely die from thermal stress and disease.[3]

The upper critical thermal limit for adult Atlantic salmon is around 25°C (77°F), while for juveniles it ranges from 22-33°C (71.6-91.4°F), with 27.8°C (82°F) being the lethal temperature for parr.[1]

Salmonids have the lowest thermal tolerance among fish species, with maximum upper lethal temperatures barely exceeding 25°C (77°F) for the family.[1] Warm water reduces available oxygen, increases susceptibility to diseases/predators, and can trigger metabolic issues like lactic acid buildup.[1][3]

In summary, while the optimal river temperature for salmonids is 55-64°F (12.8-17.8°C), temperatures over 68°F (20°C) become increasingly stressful, with 77°F (25°C) being critically lethal for extended exposures.[1][3]

Citations:
[1] https://waves-vagues.dfo-mpo.gc.ca/library-bibliotheque/348301.pdf
[2] https://www.trrp.net/restoration/adaptive-management/water-temperature/
[3] https://www.wildsalmon.org/news-and-media/sos-blog/hwr-2023-issue-2.html
[4] https://www.fs.usda.gov/rm/pubs_other/rmrs_2001_dunham_j001.pdf
[5] https://stateofsalmon.wa.gov/statewide-data/water/