I used to troll with an 8HP Suzuki 2 stroke on my 17 foot Whaler when I lived in Washington State, 90% of time it was for salmon in the saltwater and it sure didn't bother them, but it was deep trolling with downriggers.
A couple of times a year I would troll for trout and kokanee in freshwater, sometimes with a downrigger, but shallow, 15 feet or so, or just long lining the lure. Caught plenty of fish, but would run the iures about 100 feet behind the boat.
Walleye trolled a couple of times and also had success.
If you ever watch any of the walleye shows where they are trolling, they almost always use gas motors. If I was to get back into serious trolling, I'd have a gas kicker.