I have two labs and they are my excuse to get out of the house. They were trained to go fishing however and do not spook fish. I also fish where there isn't a lot of people so they are not bothering others.
They know exactly what is going on and when they hear a rise or see me stocking a pool they go right into stealth mode. I can concentrate 100% on fishing and not give a thought to them wandering off or plunging in the water. They stay on shore even when I am wading and they truly enjoy when I hook into one. They come over for a sniff and especially like watching them swim off when released.
I fish a lot in big cat and bear country and appreciate the extra sets of eyes not to mention their noses. I wouldn't feel comfortable without them and their enjoyment of the adventure afield is a very big part of why I fish.
The trick is to teach a dog how to fish before introducing him/her to hunting. When they understand their role and behave accordingly they are a pleasure to fish with.