I got an interview with Environment Washington to "Save the Orcas'' a couple weeks ago. Sounds cool. I figured I would be on the streets or phonebanking. Then I did background research and found the story to be a lot more complicated.
The Chinook Salmon population do have a major effect on Southern Resident Whale populations. NOAA says recent scientific information and analyses "strongly suggest that Chinook salmon abundance is very important to survival and recovery of Southern Resident killer whales" . The issue is that Snake River salmon are the ninth group ranked by spatio-temporal overlap within the Puget Sound -- essentially the likelihood for being prey -- in the Priority Chinook Stocks Report (2018) . Northern / Southern Puget Sound, Lower Columbia, Strait of Georgia, Upper Columbia & Snake Fall fall runs are ranked higher and Fraser and Lower Columbia spring runs ranked higher than the fall-spring combined Snake River Run.
Moreover, the Chinook counts from Snake River are increasing, not decreasing, in recent years. A report from 2021 states that the Spring Chinook salmon run for the Snake River concluded with 29,634 salmon passing the Lower Granite Dam. This is a 27 percent increase from 2020 levels and 55 percent larger than 2019 returns. It's from a right wing policy group, so I was initially skeptical, but it cites data from Columbia Basin Research's DART program which looks reliable.  These two facts combined were enough to convince me breaching the dams was the wrong approach to take.
NOAA has evaluated a petition to delist Snake River Fall-run Chinook Salmon as a threatened species in 2015, and actually concluded their status was still warranted. Yet there's a lot of useful links from there to read, especially the 12-month FAQ, which says their "rating for abundance and productivity is now considered “low risk,” as is its rating for spatial structure. Diversity is still considered “moderate risk"   .
I also found reports on efforts being made to address this issue on the official dam website, such as fish cooling systems recognized to be critical for the survival of salmon returning upstream to their natal spawning grounds, and about how important these four dams are to providing clean energy (about 800,000 homes at 1000 mW) 
I read a few more articles, about Mike Simpson's plan which would involve breaching the dams and which Inslee opposes, and also arguments specifically about the salmon population (https://www.wildsalmon.org/facts-and-information/why-remove-the-4-lower-snake-river-dams.html) (https://www.nwpb.org/2021/05/14/one-idea-to-remove-snake-river-dams-may-be-dead-in-the-water-inslee-and-murray-oppose-it/), but none of them got around the fact that Snake River salmon are not really critical to orca diets, and that Snake River salmon counts are increasing, not decreasing. I kind of see the Snake River salmon advocacy groups as having roped in less informed groups. I believe that breaching the dams would absolutely be a net positive for genetic diversity and abundance w.r.t. salmon but the costs are not worth it at the moment.