Study and know the law first, and operate within it.
Then, with cell phone ready approach any fisherman you suspect is a problem and then ask to see their fishing license. If you suspect that they are fishing commercially ask to see their commercial fisherman's license. If they fail to produce either of these then call the Ministry of Natural Resources. Here are some contact numbers:
Ministry of Natural Resources
Carleton Place District
10 Findlay Avenue
Carleton Place, Ontario, Canada
MNR Carleton Place 613-257-5735
MNR Ottawa 613-258-8204 (new)
MNR Brockville 613-342-8524
MNR Toll-free 1-800-267-7901
MNR Toronto 705-740-1529
Or call the local police. These fishermen are fishing illegally. Stay there until the police arrive or until the fishermen leave the spot. If you are so inclined then follow them to make sure they do not set up somewhere and continue their illegal behaviour.
Rinse and repeat.
You want the law on your side. You don’t want to give Susan Eng and Avvy Go an excuse to sick the law on you like a rabid pit bull meanwhile those they seek to protect act illegally themselves. If my suspicions are correct then many of these problem fishermen are fishing without a license and if they have a license then they are fishing commercially with a recreational license. Resorting to "nippertipping" is illegal but so is fishing without a license. Make sure Canada’s recreational and commercial fishing laws are enforced in your area. Once your town establishes the reputation that it does not tolerate illegal fishing practices I’m certain the problems will diminish. And there will be nothing Susan Eng or Avvy Go can do about it.