I was writing on a smart phone earlier and made many small errors, but the gist of it is wolves allow deeper, cooler, cleaner streams that don't freeze as deeply in winter. This results from banks and vegetation not being beaten down by ungulates, when predation keeps them from staying and browsing the banks.
The effects are synergistic; shallow water with high turbidity / sediment heats up quickly, which kills fish. Colder, deeper water also holds more oxygen than warmer, shallower water. Turbidity gives sunlight something to act on further yet heating the water. Then combine winter freezes of shallow streams, and violent runoff events unchecked by the natural sponge of dense vegetation and everything gets worse again. All the negatives form when ungulates can hang around stream banks without pressure, anyone who has had livestock knows the effect. Wolves check this and the ripple effect is startling with how far it goes, there are big changes in the forests in Yellowstone too since the reintroduction of wolves.
We have become accustomed to populations of elk and deer that in many areas are far higher than natural, moose too out east in places, sometimes where they never even existed before. We see all wild animals as a good thing, and a good sign for an ecosystem, when sometimes the balances indicate significant problems, as in Saskatchewan's Cypress Hills, which not long ago in history had grizzlies. Wolves ranged the prairies in abundance not long ago, and even the lower mainland BC / Vancouver was populated by grizzlies and wolves in a blink of history ago. No indicator is better for the health of an ecosystem than the status of its apex predators; grizzles, cougars, wolves. Up north include polar bears. When they decline, things are in serious trouble. I hunt wolves, but only where it makes sense, up north they are in extreme abundance. Down south where all the human pressure is I honestly believe they deserve a break and I'm happy to see them down there.