LC-26 · Environment
Prior appropriation of water
First in time, the river runs dry
In ordinary words
In much of the western United States, the oldest water right wins. A senior right can keep diverting while a river, and the people and fish downstream, go dry.
Why people call it a crime
Taking the whole river looks like theft from everyone else. The water code calls it a property right older than the neighbors.
A scene, not a hypothetical statute
A farm’s 1890 right calls the river. A town incorporated in 1950 cuts back. The stream gauge hits zero. The engineer is enforcing the priority date.
In legal terms
Prior appropriation — “first in time, first in right” — is the backbone of western state water law, distinct from eastern riparian sharing. Rights are usufructuary: use it or lose it, subject to beneficial-use limits. Interstate compacts and the Colorado River shortage rules add federal overlays. Senior calls are enforced by state engineers.
States adopted appropriation in the mining era to give certainty to diverters. Seniority is the point of the system, not a bug in it.
State water codes (e.g. Colo. Rev. Stat. § 37-92-101 et seq.); Colorado River Compact (1922).
Where it stops being legal
Diverting without a right, wasting water in violation of beneficial-use rules, or ignoring a compact curtailment is unlawful. Tribal reserved rights and federal reserved rights can be senior even when recognized late.