The hatchery outlet water is probably a lot warmer than the river. It is diverted from a small creek, then sits in the rearing ponds warming up, then is discharged back to the river in a not-so-appealing condition. Fish could very well give a pass to Reiter and move into the upper river, either N or S fork, in search of cooler water more than higher O2 concentration, altho cooler water does hold more O2 at saturation.

Sincerely,

Salmo g.