Document ID: ./input/supremecourt_opinions/opinions/21pdf/143orig_1qm1.pdf
Page Number: 2

MISSISSIPPI v. TENNESSEE 

Syllabus 

558 U. S. 256, to disputes over interstate river basins, see Florida v. 
Georgia,  585  U. S.  __,  __,  and  in  situations  where  the  pumping  of 
groundwater has affected the flow of interstate surface waters, see Ne-
braska v. Wyoming, 515 U. S. 1, 14.  The Court has also applied the 
doctrine to anadromous fish that migrate between the Pacific Ocean 
and  spawning  grounds  in  the  Columbia-Snake  River  system, 
“travel[ing] through several States during their lifetime.”  Idaho ex rel. 
Evans v. Oregon, 462 U. S. 1017, 1018–1019, 1024.   

The Court has not before addressed whether equitable apportion-
ment 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 con-
cerned 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 Aq-
uifer 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. 

(b)  The Court rejects Mississippi’s contention that it has a sovereign 
ownership right to all water beneath its surface that precludes appli-
cation  of  equitable  apportionment.   The  Court  has  “consistently  de-
nied” the proposition that a State may exercise exclusive ownership or 
control of interstate “waters flowing within her boundaries.”  Hinder-
lider v. La Plata River & Cherry Creek Ditch Co., 304 U. S. 92, 102. 
Although the Court’s past equitable apportionment cases have gener-
ally concerned streams and rivers, no basis exists for a different result