How will the federal government control unauthorized use (trespass) on private land within the river corridor?

Administering agencies do not have any authority to control public use of private lands. Granting of access remains the owner’s responsibility and trespass is handled by local law enforcement authorities. Federal river-administering agencies do, however, work closely with landowners to minimize problems through brochures and maps, signs, etc., and many landowners feel they are better off with the agency taking some responsibility.

Source
Interagency Wild & Scenic Rivers Council