When you are fishing a trout stream by working upstream and not seeing or spooking any trout you might be following another angler. Look for clues like pockets of still muddy water, or wet boot prints on rocks, or boot prints in the sand. If you see these clues, or if you do happen to catch up to someone who is fishing slower, leave the water immediately and go much further up the stream before re-entering. Walk at least as far as you could fish that stream in an hour, leaving them plenty of undisturbed water.
If you are within ear shot, be courteous by telling that angler how far up the stream you plan to go, so they will know. They may have some information to share with you as well like how long they intend to fish, or what is working, or how many other anglers have passed ahead of you, etc. Always be friendly on a stream and not confrontational! I have met anglers who are antagonistic and it takes away my fun.
Likewise, if you are working the stream by fishing downstream and you encounter another angler working upstream, yield the water to that angler. I am told that this is an old rule of thumb, but if it is or not, it is a scenario where neither of you are going to see much action so why not yield?
Finally, avoid the temptation of using the stream as a path by walking on the bank as much as possible. Leave the stream and the pools quietly so as not to disturb as many trout. Then the pools will not need as much time to fully recover for the next angler which may, by the way, be you.
Fishing ethics have been a favorite topic of mine for some time and to see my list of the top ten rules for good etiquette please go to the Trout University blog Fishing Ethics.