not 100%, but belive that once you have it, you always have it. it just "acts up" every now and again.
I will refrain from examples , Im sure someone will list them
it also comes from fecal matter, found down stream from grazing sheep, cattle, and beaver.
my attitude, is "if you can see the source, its fine". that means snow field run-off, or spring.
"seeing" a waterfall dosn't count as the "source"
Rn's, and Docs please chime in....
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