Page:Mississippi v. Tennessee (2021).pdf/12

Rh the aquifer that underlies Mississippi. Kansas v. Colorado, 206 U. S., at 97. Tennessee’s pumping has contributed to a cone of depression that extends miles into northern Mississippi. Hearing Tr. 484–485, 501–502, 926; see also Report of Special Master 22–23. Mississippi itself contends that this cone of depression has reduced groundwater storage and pressure in northern Mississippi. See Complaint ¶¶25, 54. It also alleges that Tennessee’s pumping is “siphoning” tens of millions of gallons of groundwater each day from Mississippi’s portion of the aquifer. Id., ¶54. Such interstate effects are a hallmark of our equitable apportionment cases. See, e.g., Florida v. Georgia, 592 U. S., at ___–___ (2021) (slip op., at 2–3) (examining the effects of Georgia’s water use on Florida’s oyster fisheries and river ecosystem).

For these reasons, we hold that the waters of the Middle Claiborne Aquifer are subject to the judicial remedy of equitable apportionment.

Mississippi contends that it has sovereign ownership of all groundwater beneath its surface, so equitable apportionment ought not apply. We see things differently. It is certainly true that “each State has full jurisdiction over the lands within its borders, including the beds of streams and other waters.” Kansas v. Colorado, 206 U. S., at 93. But such jurisdiction does not confer unfettered “ownership or control” of flowing interstate waters themselves. Wyoming v. Colorado, 259 U. S., at 464. Thus, we have “consistently denied” the proposition that a State may exercise exclusive ownership or control of interstate “waters flowing within her boundaries.” Hinderlider v. La Plata River & Cherry Creek Ditch Co., 304 U. S. 92, 102 (1938). Although our past cases have generally concerned streams and rivers, we see no basis for a different result in the context of the Middle Claiborne Aquifer. When a water resource is shared between several States, each one “has an interest which