I don't use a filter, or treat water, but I wouldn't drink out of the Crooked River at Smiff either. I drink tap water.
Statistically, one person can drink water with minimal chance or getting sick, but if thousands drink that water, 10 or so are gonna get sick. Its like playing the lottery except chances are, you will win. But it sux to lose.
The higher the fresher thing only applies in that there is less source area above to source contaminate. But high is not necessarily safe. Local factors, like someone who just came back from Nepal taking a dump at a campsite 1km upstream, take a greater role in determining infection. I know from water tests I have done that fecal colifom loads in typical below treeline BC stream water are generally in the 1-5 bacterial count, but randomly spike up to 1000 level counts in a small proportion of samples. Where there's fecal coliform, there's potential for disease, and giardia and crypto counts usually, but not always, follow the same trend.
I would assume many alpine areas in WA to have a slightly higher count due to their greater use, eg Snow Creek or the creek near W side of Lib Bell probably has a higher coliform count than Tretheway Creek at the head of Harrison Lake does.