This is how hatchery fish have a negative impact on wild fish.

The Progeny of hatchery fish spawning in the wild have an extremely low survival rate. The same poor survival occurs when a wild fish spawns with a hatchery fish. This has even been documented in the progeny of first generation hatchery brood stock. (offspring of wild fish spawned in a hatchery).
The biggest problems occur when hatchery fish spawn inplaces that have small populations of wild fish. The hatchery fish simply spawn with so many wild fish that is reduces the effectivness of the wild fish in reproduction.

Here on the Washougal river the fish have survived 2 huge forest fires, 3 dams,large mining operations, siltation from bad logging practices, a papermill that dumped their waste into the river, angler overharvest and a host of other things. The one thing that Washougal native stock could not survive was the Skamania hatchery. Even into the 50-early 60's the population of wild Washougal steelhead was holding it's own at around 1500. As soon as the hatchery went in thoes numbers declined and as the hatchery produced more and more the numbers declined fasrer. Now even with WSR regulations runs of wild fish in the 100-300 range are the norm.
Conversly the elimination of hatchery dteelhead from the wind river has led to rapidly increasing numbers of wild steelhead. down from a lows in the 20-40 range the retuen lase summer was 240 and expected to be 400 this year. All it took was the elimination of the hatchery plants.

In the years after the Mountain exloded the South Toutle was the only river in southwest Washington to be meeting it's escapement goals for winter steelhead.
after a few years of being healthy WDFW started planting hatchery summer runs. As soon as they did the wild winter run began to decline and now no streams in southwest Washington are meeting escapement goals.
It seems clear to me that hatchery steelhead do more harm than good and should only be used in areas where they can be removed from the system prior to spawning.