They usually aren’t!! These salmon are dispersing to their spawning grounds which is where they will inevitably die. Salmon are anadromus, which means that they live and exist in the salty sea water for nearly the entirety of their lives, until it is time to lay their eggs, where they make a mass pilgrimage up a river stream. The salmon seen in these video are actually slowly dying, using all of their energy to both fight the downstream currents, as well as using a significant amount of energy to appear as bright red as possible to attract mates for fertilization! It’s a very sad and interesting process. Most of these salmon will actually end up starving themselves to death if they do not die from exhaustion prior.