Opinion of the Court
Following motions practice, discovery, and a five-day evidentiary hearing, the Special Master issued a report recommending that we dismiss Mississippi’s complaint, but with leave to amend. He first determined that the Middle Claiborne Aquifer is an interstate water resource. He found that the aquifer is a “single hydrogeological unit,” that Tennessee’s pumping affects groundwater beneath Mississippi, and that prior to such pumping, “groundwater flowed between Mississippi and Tennessee”—a fact Mississippi “does not dispute.” Report of Special Master 15–24.
The Special Master then concluded that, because the aquifer is an interstate water resource, equitable apportionment is the appropriate remedy. He recognized that equitable apportionment “stands alone as the federal common-law principle for disputes over interstate water,” id., at 31, and saw “no compelling reason to chart a new path for groundwater resources,” id., at 26. Because Mississippi’s complaint did not seek equitable apportionment, the Special Master recommends that we dismiss it. But he also recommends that we grant Mississippi leave to file an amended complaint seeking equitable apportionment, though the State has not yet sought such leave.
Mississippi and Tennessee both filed exceptions to the Special Master’s report. Mississippi objects to the Special Master’s recommendation that we dismiss the suit. It argues that the Special Master erred in finding the water in the Middle Claiborne Aquifer subject to equitable apportionment. Tennessee objects only to the Special Master’s recommendation that we grant Mississippi leave to amend its complaint.
We “conduct an independent review of the record, and assume the ultimate responsibility for deciding all matters.” Kansas v. Nebraska, 574 U. S. 445, 453 (2015) (internal quotation marks omitted). Based on that review, we dismiss Mississippi’s complaint and decline to grant leave to amend.
