There isn't a concrete answer to this one ... but the rule of thumb is to avoid the water that the wading angler is fishing ... for a gear angler, that may mean a slot in the middle, or on the far side, for a fly angler, it may mean the water just out and below that he / she is swinging through. Try to observe where the angler is working the water and pass accordingly. If in doubt, ASK!!!! I've heard lots of guys think that I'm mean because I have given offending boats more than gentle reminder that they've run over the water that my clients are trying to fish ... personally, I do think it makes a difference, especially in clear water ... besides that it is just plain rude whether it bothers the fish or not! And a hint for those I (as well as many other guides) pass on the Peninsula rivers, figure that we just ran over the spot where the fish are LEAST likely to be ...