Wyo. Stat. § 41-4-323: Surplus water; senior priority.

When anyone has applied surplus water to beneficial use, as herein provided, he shall be entitled thereafter to divert and beneficially use his proportionate share thereof, and such diversion and beneficial use, when accomplished, is hereby declared to be an appropriation of such water, entitled to a priority senior to any water right acquired after March 1, 1945.