In ignoring the adage, "pigs get fed, but hogs get slaughtered," the lake owner has probably succeeded in buying a truckload of litigation by simply asking too much from the property owners. I am sure there are many attorneys in the Valpriso area who would represent the homeowners for only $5K each!
I would research restrictive covenants and reciprical easements (which are every much a property right as the property rights of the fee owner), as well rights under the law of adverse possession and prescriptive easements. (Although adverse possession/prescriptive easement usually requires an adverse and notorious use over a 10 or 20 year period, those requirements are often satisfied absent an express grant of permissive use.) I would also look at the right of redemption.