Wyo. Stat. § 41-3-201
All that part and amount of the waters of an interstate stream which, unless prevented by artificial barrier, will enter the state of Wyoming from another state while flowing in a natural stream channel, and which have been, or may hereafter be, determined by final decree of the supreme court of the United States not to be available for diversion and application to beneficial use within the state of Wyoming, or other waters originating outside of the state of Wyoming, and which neither the state of Wyoming nor any Wyoming appropriator could divert and use as against another state or appropriators therein, the rights to which through purchase, exchange or negotiation are acquired by anyone for beneficial use in the state of Wyoming, and which are conveyed, imported or permitted to flow into the state of Wyoming through the channel of any natural stream, or otherwise, are, for the purposes of this act, hereby defined as "foreign water".
W.S. 41-3-201