There is no need for confrontation. No need to educate a poacher or warn them of fines.
Its plain and simple. You see a few suspect fish on the way back to the parking lot, you sit down on the tailgate, power up your phone, call 1-800-831-1174 and make a report. I've done it. It only takes a few minutes. You don't have to stay on the line until the officer arrives. They may come, they may not come, but you've done your part.
Even if the fish turns out to be legal, at least you've got an officer down there checking trout stamps.