Interstate Compacts and Equitable Apportionment
No state owns a river that leaves it. The share each one gets is set by an agreement Congress consented to, by a decree entered in the Supreme Court's original jurisdiction, or occasionally by statute, and every user inside the state is subordinate to that ceiling.
The rule in short
Rivers crossing state lines are divided in three ways: a compact negotiated by the states and consented to by Congress, an equitable apportionment decreed by the Supreme Court, or an apportionment enacted by statute. A consented compact becomes federal law and cannot be altered by one state. Enforcement lies in the Court's exclusive original jurisdiction over controversies between states.
A river does not stop at a state line and neither does the conflict over it. Three mechanisms divide interstate waters: a compact negotiated between the states, an equitable apportionment decreed by the Supreme Court, or an apportionment enacted by Congress. Whichever applies operates as a ceiling above every permit, decree and district allocation inside each state.
Making a compact, and what it becomes
Negotiation is conducted by commissioners appointed by each state, usually with a federal representative appointed by the President who participates without a vote. The negotiated instrument is then ratified by each state legislature and submitted to Congress, whose consent the Compact Clause requires for an agreement between states.
Consent changes the instrument's character. A compact consented to by Congress is federal law as well as an agreement, so it preempts inconsistent state law, cannot be repealed or amended by one state acting alone, and is construed by federal courts as a statute rather than by the courts of either state. A state that finds a compact burdensome has two options: renegotiate with the other party and return to Congress, or perform.
The operative terms
Allocation formulas vary. Some compacts divide flow by percentage, some fix an annual volume for each state, some impose a delivery obligation measured at a specified gage, and some allocate by irrigated acreage or by depletion rather than by diversion. Nearly all provide for measurement points, accounting rules, and a commission to administer them.
The remaining terms are where the difficulty lives: how shortage is shared in dry years, how storage is credited, whether deliveries are measured annually or on a running average over several years, how depletions from groundwater pumping are computed, and whether the compact disclaims any effect on federal and tribal claims. A compact drafted around the hydrology of a wet period can obligate a state to deliver water that does not exist in a dry one.
A delivery obligation is the state's, not any individual user's, but the state can only meet it by controlling its own diverters. That produces the compact call: where deliveries fall short, the state curtails water rights junior to the compact, sometimes across an entire subbasin, using the ordinary administration machinery. Users whose permits are perfectly valid under state law are shut off because of an obligation they were never party to, and the curtailment order is enforceable in the same way as any other.
Apportionment by decree
Where no compact governs, a state may invoke the Supreme Court's exclusive original jurisdiction over controversies between states and ask for an equitable apportionment. The Court weighs physical and climatic conditions, the consumptive use in each state, the character and rate of return flows, the extent of established uses and the harm from disrupting them, the availability of storage, and the practical effect of wasteful practices.
The burden is heavy. A complaining state must show real and substantial injury by clear and convincing evidence, and the Court has repeatedly declined to disturb established uses in the absence of that showing. Priority is a factor rather than the rule, since applying strict priority across a state line would let one state's earliest appropriators consume everything.
The mechanisms compared
| Mechanism | Who decides | What it divides | How it changes | Remedy for violation |
|---|---|---|---|---|
| Interstate compact | The states, with congressional consent | Flow, volume or delivery at a gage | Renegotiation plus new consent | Original action in the Supreme Court |
| Equitable apportionment | The Supreme Court | Shares of the usable supply | Motion to modify the decree | Enforcement of the decree, contempt |
| Congressional apportionment | Congress by statute | Volumes fixed in the act | Amendment of the statute | Suit to enforce the statute |
| General stream adjudication | A state court or agency | Rights within one state | Continuing jurisdiction of the court | Curtailment by the water master |
The last row is included because it is constantly confused with the others. An adjudication cannot enlarge a state's share, and a decree entered inside a basin-wide state proceeding is subject to the interstate allocation whether or not it says so.
Suing a state, and what a decree can order
An original action begins with a motion for leave to file a bill of complaint. The Court, if it grants leave, appoints a special master who takes evidence, holds hearings and files a report with recommended findings. Parties file exceptions, the Court hears argument on them, and it enters a decree. The proceedings are slow by design and expensive in fact, and states settle a large share of them before judgment.
Remedies include a decree directing compliance, injunctive relief limiting depletions, and money damages for water that should have been delivered and was not. Because the harm is often historic and the water cannot be returned, damages calculated on the value of the shortfall have become the practical remedy in several cases.
Compliance in the field depends on the same tools every water user encounters. The state administers its own users under priority rules, accounts for well pumping under conjunctive management because depletions from wells count against deliveries just as diversions do, and absorbs quantified federal and tribal reserved rights within its share rather than in addition to it. A compact is therefore not a document that sits above the system; it is the constraint that explains why the system behaves the way it does in a dry year.
Points to carry away
- An interstate compact requires legislative ratification in each state and the consent of Congress.
- Once consented to, a compact is federal law and cannot be modified by one state's legislation.
- The Supreme Court has exclusive original jurisdiction over controversies between two or more states.
- Equitable apportionment applies where no compact governs, and requires proof of real and substantial injury.
- Compliance is normally measured at a designated gage, annually or on a multi-year running average.
- A state must curtail its own users to meet a delivery obligation it has undertaken.
Questions readers ask
Can an individual water user sue to enforce a compact?
Usually not directly. A compact is an agreement between states, and enforcement in the Supreme Court's original jurisdiction is available to the states themselves. Some compacts create an administrative commission with enforcement powers and a procedure open to water users, and a user may sometimes raise a compact as a defense or as a limit on state action in ordinary litigation. Where a user's real complaint is that the state has over-allocated internally, the remedy is a state proceeding, not an interstate one.
What does a compact commission actually do?
It administers the accounting. A commission typically comprises one or more commissioners from each state and often a federal representative who chairs without a vote, and it adopts the rules by which flows, diversions and deliveries are computed. It resolves technical disputes about gage records and depletion estimates, publishes annual accounting, and in some compacts approves projects or storage operations. It is not a court, and its decisions are subject to whatever review the compact and the states provide.
Are federal and tribal rights charged against a state's share?
Generally yes. Reserved rights within a state are ordinarily counted against that state's apportionment rather than added on top of it, so a large tribal quantification reduces what remains for other users in the same state. Compacts sometimes address the point expressly, and some disclaim any effect on federal or tribal claims, which leaves the allocation question to be resolved later. The interaction is one of the most consequential open questions in several basins.
Sources
- Cornell Legal Information Institute — 28 U.S.C. 1251, Original jurisdictionThe Supreme Court's exclusive original jurisdiction over controversies between two or more states.
- Cornell Legal Information Institute — U.S. Constitution, Article IThe Compact Clause, requiring the consent of Congress to an agreement between states.
- Cornell Legal Information Institute — 43 U.S.C. 666, Suits for adjudication of water rightsThe separate consent to joinder in intrastate adjudications, distinct from interstate suits.
- Supreme Court of the United StatesThe forum for original actions between states, including compact enforcement and apportionment.
- U.S. Geological Survey — Water ResourcesStreamflow measurement programs supplying the records compacts are administered on.
- USGS National Water Information SystemThe gage data used to compute deliveries and to prove or disprove a shortfall.
Lawwise is a publication, not a law firm. This article states general rules and cites its sources; it is not advice about any particular case, and the law differs by state and changes over time.
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