Are motorized vehicles allowed within designated wild and scenic river corridors?

Yes. Motorized access allowed prior to designation will, generally, be allowed post designation, subject to congressional intent and river management objectives. However, if motorized use adversely impacts a river’s water quality or outstandingly remarkable values, or if the use is not consistent with the river’s classification the route may be closed or regulated.

The continued legality of motorized use on land or water is best determined through the river management planning process, which considers factors such as impacts on river values, user demand for such motorized recreation, health and safety to users, and acceptability with desired experiences and other values for which the river was designated.

Source
Interagency Wild & Scenic Rivers Council