50 CFR 25.52: Designation.

To be designated as an “Entrance Fee Area”, a unit of the National Wildlife Refuge System must be found to demonstrate that:

(a) The level of visitation for recreational purposes is high enough to justify the collection of fees for admission permits for economic reasons;

(b) There is a practical mechanism in existence for implementing and operating a system of collecting fees for admission permits; and

(c) Imposition of a fee for admission permits is not likely to result in undue economic hardship for a significant number of visitors to the unit.