Neb. Rev. Stat. § 61-213

Water division No. 1 shall consist of (1) all the lands of the state drained by the Platte Rivers and their tributaries lying west of the mouth of the Loup River and (2) all other lands lying south of the Platte and South Platte Rivers that may be watered from other superficial or subterranean streams not tributary to the Platte River.