Wyo. Stat. § 41-3-501: Water divisions defined.

(a) The state of Wyoming is hereby divided into four (4) water divisions, as follows:

(i) Water Division No. 1 shall consist of all lands within this state, drained by the North Platte River, and the tributaries of the North Platte River and the South Platte River, Snake River, (a tributary of Green River) and its tributaries, and Running Water Creek and its tributaries;

(ii) Water Division No. 2 shall consist of all lands within this state, drained by the tributaries of the Yellowstone and Missouri Rivers north of the water shed of the North Platte River and Running Water Creek, and east of the summit of the Big Horn Mountains;

(iii) Water Division No. 3 shall consist of all lands within this state drained by the Big Horn River and its tributaries, and by Clark's Fork and its tributaries;

(iv) Water Division No. 4 shall consist of all lands within this state drained by the Green, Bear and Snake Rivers, and the tributaries thereof; except Snake River, (a tributary of Green River), and its tributaries.