It won't selectively kill fish, it'll kill frogs, turtles, algae, and anything else that lives in the water which isn't a bacteria or archaea capable of living in an anoxic environment. Possibly also the predators of those species which live on land.
> it'll kill frogs, turtles, algae, and anything else that lives in the water which isn't a bacteria or archaea capable of living in an anoxic environment
That's a bit dramatic. Frogs, turtles, salamanders, etc, can breathe air.
The only predators are birds, who can find food at any of the many other lakes in the area.
Crater Lake's geography is essentially unique among lakes that may be having this issue. There is a near-total lack of native fauna that would be affected by an anoxic event.
