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Wyoming v. Colorado, 259 U.S. 419 (1922)

Why this matters: The Court took prior appropriationprior appropriationThe western US rule. Whoever first took water and put it to use has the strongest claim, no matter where their land sits. The shorthand is "first in time, first in right.", a doctrine invented in mining camps, and applied it across a state line. Priority now outranked sovereignty. It is also the case that scared the western states into negotiating the Colorado River CompactcompactA binding agreement between states that Congress approves. Once approved it becomes federal law and overrides conflicting state rules. The Great Lakes Compact is one. that same year.

Doctrine: Interstate equitable apportionmentequitable apportionmentThe US Supreme Court dividing an interstate river between states that cannot agree. The evidence bar is very high. Florida spent over a decade and lost., prior appropriationprior appropriationThe western US rule. Whoever first took water and put it to use has the strongest claim, no matter where their land sits. The shorthand is "first in time, first in right."

Case name and citation

Wyoming v. Colorado, 259 U.S. 419 (1922).

Court and year

Supreme Court of the United States, original jurisdiction. Decided June 5, 1922.

One-line holding

Where both states follow prior appropriation, the Court will apply that doctrine across the state line, so Wyoming’s senior appropriations on the Laramie River defeat Colorado’s proposed junior transbasin diversiondiversionMoving water out of the Great Lakes basin. The Compact bans new ones except in a few narrow cases..

Facts

The Laramie River rises in Colorado and flows north into Wyoming.

Colorado planned a large diversiondiversionMoving water out of the Great Lakes basin. The Compact bans new ones except in a few narrow cases. from the headwaters, carrying water out of the Laramie basin to irrigate Colorado land in a different drainage.

Wyoming had extensive existing irrigation appropriations downstream, and they were older than the proposed Colorado project. Wyoming sued to stop the diversion.

Colorado’s position was sovereign and blunt: as a state, it could dispose of any part or all of the water flowing within its borders as it chose.

Both states ran on prior appropriation, and both had written the doctrine into their constitutions.

When both states follow prior appropriation, does the Court apportion an interstate stream by applying that shared doctrine across the boundary, or by some other measure of equity between sovereigns?

Holding and reasoning

The Court rejected Colorado’s sovereignty argument outright. An upstream state does not own the river in a way that lets it divert without regard to injury downstream.

It then held that appropriation “furnishes the only basis which is consonant with the principles of right and equity applicable to such a controversy.”

The reasoning rested on shared expectations. Each state applies and enforces priority in its own territory. It’s the rule intending appropriators “naturally would turn for guidance.” Both states call the rule just, both wrote it into their constitutions, and the doctrine originated in local custom before either state existed.

So the Court applied the cardinal rule directly across the line: priority of appropriation gives superiority of right, and state boundaries do not reset the clock.

Colorado’s diversion was limited to what could be taken while leaving enough in the river to satisfy Wyoming appropriations senior to it.

Why it matters

Read this next to Kansas v. Colorado (1907) and the difference is the whole story of equitable apportionmentequitable apportionmentThe US Supreme Court dividing an interstate river between states that cannot agree. The evidence bar is very high. Florida spent over a decade and lost.. See 1907-kansas-v-colorado.md.

In 1907 the 2 states had different systems, so the Court balanced equities and the complaining state lost. In 1922 they shared a system, so the Court just ran the priorities, and the complaining state won.

The alarm this caused is the real historical legacy. If interstate priority controlled, then the fast-developing lower basin states, especially California, could establish senior rights on the Colorado River and permanently subordinate the slower-growing upper basin.

The upper basin states did the math and moved. The Colorado River CompactcompactA binding agreement between states that Congress approves. Once approved it becomes federal law and overrides conflicting state rules. The Great Lakes Compact is one. was negotiated in 1922, the same year, and signed that November. It divided the river between basins by volume rather than by priority, precisely to escape the rule this case announced.

So the most consequential effect of Wyoming v. Colorado is a compact written to avoid it.

What it means for a landowner today

No application to a Wisconsin parcel. Wisconsin has never followed prior appropriation, so the shared-doctrine premise of this case doesn’t exist here.

The transferable insight is about compacts. Interstate water agreements are usually defensive. They exist because at least one party feared what a court would do.

That framing helps in reading the Great Lakes Compact. Its diversion ban is not a neutral technical rule. It’s 8 states agreeing to a bright line so that no state has to litigate against another’s growth. See ../03-wisconsin-great-lakes/.

And when a compact is silent on something, don’t assume the silence creates a right. The Court read compact silence narrowly in Tarrant Regional Water District v. Herrmann (2013). See 2013-tarrant-v-herrmann.md.

Subsequent history / is it still good law

Good law as of July 2026 for the proposition that the Court may apply prior appropriation across state lines when both states follow it.

The decreedecreeThe court order at the end of an adjudication, spelling out exactly who gets how much water and in what order. itself was modified in later proceedings, and the Laramie River is now administered under those modified terms.

The doctrine has evolved since. Modern equitable apportionment weighs a broader set of factors, and a complaining state must prove injury of serious magnitude by clear and convincing evidence. Florida v. Georgia (2021) is the current statement of that burden. See 2021-florida-v-georgia.md.

Most major western rivers are now governed by compacts rather than by judicial apportionment.

Sources

Research demo, not legal advice. Facts current as of July 2026. Water law is state-specific and moves quickly, so confirm anything you plan to act on with a licensed attorney and the relevant state agency.