Tough issue for me, not only because of the Amish families my family has been friends with for 25 years, but also because I see enough of some ethnic groups that are no-licenses, over-limit fishermen.
I've never fished with the Amish but they sure are happy when I share fish and return the favor with farm grown food.
Could the "English" or non-Amish be dressing up in Amish garb as part of their poaching scheme.(:

Solution- Alert your local WCO about the place and individuals so he patrols. Especially if it is a consistent pattern. It'll be out of your hands and you'll know you have done what you can within your limits as an angler.

Please - No Amish lynch mobs. Plenty of people think the rules don't apply to them. sit at a stop sign and see how many people don't even slow down.