Mississippi v. Tennessee
The Facts
The Memphis Sand Aquifer, one of the largest freshwater aquifers in the United States, underlies both Mississippi and Tennessee. Memphis's water utility pumps millions of gallons daily from wells on the Tennessee side, drawing down the aquifer below the state border. Mississippi filed an original action in the Supreme Court claiming the groundwater beneath Mississippi's territory was Mississippi's property and that Tennessee's extraction constituted an unauthorized taking of that property. Tennessee argued equitable apportionment principles governed.
The Application
Mississippi's claim of exclusive ownership failed because the groundwater at issue, the Memphis Sand Aquifer, crosses state lines and is actively extracted by Tennessee, making it an interstate water resource governed by federal common law rather than state property law. The Court applied the equitable apportionment doctrine, holding that Mississippi cannot simply assert fee ownership of subsurface water but must instead demonstrate through balancing competing state interests, Tennessee's historical reliance on the aquifer, the economic needs of Memphis, and any disproportionate harm to Mississippi, whether equitable principles warrant limiting Tennessee's extraction. By dismissing Mississippi's property-based complaint, the Court clarified that the interstate nature of the aquifer's flow automatically removes it from the domain of territorial property rights and places it squarely within the federal framework designed to allocate shared water resources between competing jurisdictions.
The Conclusion
**Unanimous 2021 ruling confining groundwater disputes between states to the equitable apportionment framework rather than state property law.** Mississippi lost its claim but preserved the right to seek equitable apportionment in a properly pled case. The ruling clarifies that no state can claim exclusive ownership of interstate groundwater simply because it sits beneath state territory.
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Case Analysis
Overview
Mississippi v. Tennessee (2021) held 9-0 that Mississippi could not pursue a simple property-based claim asserting ownership of groundwater beneath the Memphis Sand Aquifer, which extends across state lines. The Court held that interstate water allocation disputes, including those over groundwater migrating across state boundaries, are governed by federal common law principles of equitable apportionment, not by one state's property law. Mississippi's complaint seeking exclusive ownership was dismissed.
Facts
The Memphis Sand Aquifer, one of the largest freshwater aquifers in the United States, underlies both Mississippi and Tennessee. Memphis's water utility pumps millions of gallons daily from wells on the Tennessee side, drawing down the aquifer below the state border. Mississippi filed an original action in the Supreme Court claiming the groundwater beneath Mississippi's territory was Mississippi's property and that Tennessee's extraction constituted an unauthorized taking of that property. Tennessee argued equitable apportionment principles governed.
Issue
Whether Mississippi could assert a simple common-law property ownership claim over subsurface groundwater that migrates across state lines, or whether such disputes are governed by the federal equitable apportionment doctrine applicable to interstate water controversies.
Rule
Federal common law governs disputes between states over interstate waters. The equitable apportionment doctrine (Colorado v. New Mexico, 1982) requires courts to balance competing states' needs, historical uses, and economic interests in allocating shared water resources. A state cannot claim simple fee ownership of flowing water that does not remain within its borders.
Analysis
Mississippi's claim of exclusive ownership failed because the groundwater at issue, the Memphis Sand Aquifer, crosses state lines and is actively extracted by Tennessee, making it an interstate water resource governed by federal common law rather than state property law. The Court applied the equitable apportionment doctrine, holding that Mississippi cannot simply assert fee ownership of subsurface water but must instead demonstrate through balancing competing state interests. Tennessee's historical reliance on the aquifer, the economic needs of Memphis, and any disproportionate harm to Mississippi. Whether equitable principles warrant limiting Tennessee's extraction. By dismissing Mississippi's property-based complaint, the Court clarified that the interstate nature of the aquifer's flow automatically removes it from the domain of territorial property rights and places it squarely within the federal framework designed to allocate shared water resources between competing jurisdictions.
Conclusion
**Unanimous 2021 ruling confining groundwater disputes between states to the equitable apportionment framework rather than state property law.** Mississippi lost its claim but preserved the right to seek equitable apportionment in a properly pled case. The ruling clarifies that no state can claim exclusive ownership of interstate groundwater simply because it sits beneath state territory.
Notes
OT2021. Added via SCOTUS bulk import 2026-05-14
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