I don't see what Federal employees (rangers) have to do with enforcing a state law. They have their hands full with actual work within their jurisdiction. Plus, I don't think rangers have the authority to write state tickets.
More to the point, having the sticker does not mean anything at this point. It's not like your gear suddenly becomes "certified zebra mussel-free" when you plop down your money.
"A river is more than an amenity, it is a treasure."
-Oliver Wendell Holmes writing for the majority in New Jersey v. New York