PRACTICABLY IRRIGABLE ACREAGE (PIA)

The standard (as established in Arizona v. California, 373 U.S. 546 (1963), decreed in final form, 376 U.S. 340 (1964), decree amended, 383 U.S. 268 (1966), second supplemental decree entered, 466 U.S. 144 (1984)) for quantifying reserved water rights on an Indian reservation set aside with the intent that its inhabitants pursue agriculture (or, assumed by extension, water-related economic pursuits, e.g., fish hatcheries). Under this standard Indian tribes are legally entitled to the amount of water needed to irrigate all practicably irrigable acreage within their reservation boundaries. Furthermore, these water rights have a priority date equal to the date at which the reservation was established. Under the Winters Doctrine, which is the foundation of this policy, practicably irrigable acreage must meet two criteria: (1) the land must be able to reasonably sustain crops; and (2) the cost of supply water to the crops must not be unreasonable. Also see Winters Rights (Decision) and Water Law (Federal).