North Raven is predominantly a brown trout river correct? If so, they are far less susceptible to whirling disease and typically won't die from it.
Good on you for keeping an eye out, the disease (if bad enough) will usually kill fish that are hatched this year, the parasite takes about 3 months after fish hatch to have a full effect and if they are badly infected during that time they will likely die from it (think about 3 inches). So survival into those larger sizes likely wouldn't happen, but that is typical of rainbows and other susceptible trout, browns less so.
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