The salmon’s journey is one of the great wonders of nature. But it is also a fragile one. Warm runoff in the rivers—shallow water can heat up quickly as it flows down out of the mountains—made it difficult for the struggling salmon to breathe (the warmer the water, the faster oxygen molecules vibrate with kinetic energy, allowing them to flee their molecular bonds and escape into the air. “It leaves fish feeling like they are breathing with a plastic bag over their heads,” one wildlife biologist told me). Their iridescent silvery skin broke out in red lesions. Cottony puffs of fungus grew on
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