# Mississippi v. Tennessee (2021)

Note: Where it is feasible, a syllabus (headnote) will be released, as is being done in connection with this case, at the time the opinion is issued. The syllabus constitutes no part of the opinion of the Court but has been prepared by the Reporter of Decisions for the convenience of the reader. See United States v. Detroit Timber & Lumber Co., 200 U. S. 321, 337.
SUPREME COURT OF THE UNITED STATES
Syllabus
MISSISSIPPI v. TENNESSEE ET AL. ON EXCEPTIONS TO REPORT OF SPECIAL MASTER No. 143, Orig. Argued October 4, 2021—Decided November 22, 2021
Mississippi brought an original action against Tennessee for damages and other relief related to the pumping of groundwater by the City of Memphis from the Middle Claiborne Aquifer, a valuable water resource that lies beneath eight States. Mississippi argues that Tennessee’s pumping—using wells Mississippi concedes are located entirely in Tennessee—siphons water away from Mississippi and amounts to a tortious taking of groundwater owned by Mississippi. Mississippi expressly disclaims any equitable apportionment remedy, arguing that the “fundamental premise of this Court’s equitable apportionment jurisprudence—that each of the opposing States has an equality of right to use the waters at issue—does not apply to this dispute.” Complaint ¶49. The Special Master appointed by the Court to assess Mississippi’s claims determined that the aquifer is an interstate water resource and that equitable apportionment is the exclusive judicial remedy. Because Mississippi’s complaint did not seek equitable apportionment, the Special Master recommended that the Court dismiss the complaint but grant Mississippi leave to amend. Mississippi challenges the recommendation to dismiss; Tennessee objects to the recommendation to grant Mississippi leave to file an amended complaint.
Held: The waters of the Middle Claiborne Aquifer are subject to the judicial remedy of equitable apportionment; Mississippi’s complaint is dismissed without leave to amend. Pp. 7–12.
The Court has not before addressed whether equitable apportionment applies to interstate aquifers. Equitable apportionment of the Middle Claiborne Aquifer is “sufficiently similar” to past applications of the doctrine to warrant the same treatment, for several reasons. Id., at 1024. First, the Court has applied equitable apportionment when transboundary water resources were at issue. Here the Middle Claiborne Aquifer’s “multistate character” seems beyond dispute. Sporhase v. Nebraska ex rel. Douglas, 458 U. S. 941, 953. Second, the Middle Claiborne Aquifer contains water that flows naturally between the States, and the Court’s equitable apportionment cases have all concerned such water, Kansas v. Colorado, 206 U. S. 46, 98, or fish that live in it, Idaho ex rel. Evans, 462 U. S., at 1024. While Mississippi contends the natural transboundary flow of the Middle Claiborne Aquifer is slower than some streams and rivers, the Court has applied equitable apportionment even to streams that run dry from time to time. See Kansas, 206 U. S., at 115. The speed of the flow does not place the aquifer beyond equitable apportionment. Finally, actions taken in Tennessee to pump water from the aquifer clearly have effects on the portion of the aquifer that underlies Mississippi. Tennessee’s pumping has contributed to a cone of depression that extends miles into northern Mississippi, and Mississippi itself contends that this cone of depression has reduced groundwater storage and pressure in northern Mississippi. Such interstate effects are a hallmark of the Court’s equitable apportionment cases, see, e.g., Florida, 592 U. S., at __. For all these reasons, the Court holds that the judicial remedy of equitable apportionment applies to the waters of the Middle Claiborne Aquifer. Pp. 7–9.
(c) Mississippi has neither sought leave to amend its complaint nor tendered a proposed complaint seeking equitable apportionment. The Court does not address whether Mississippi should be granted such leave and sustains Tennessee’s objection to the Special Master’s recommendation to grant Mississippi leave to amend. Pp. 11–12.
Exceptions overruled in part and sustained in part, and case dismissed.
Roberts, C. J., delivered the opinion for a unanimous Court.
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