Document ID: ./input/supremecourt_opinions/opinions/21pdf/143orig_1qm1.pdf
Page Number: 7.0

4 

MISSISSIPPI v. TENNESSEE 

Opinion of the Court 

Both decisions turned in large part on what is known as
“equitable apportionment.”  Under that doctrine, this Court 
allocates rights to a disputed interstate water resource af-
ter one State sues another under our original jurisdiction. 
See Kansas v. Colorado, 206 U. S. 46, 97–98 (1907).  Tradi-
tionally, equitable apportionment has been the exclusive ju-
dicial remedy for interstate water disputes, unless a stat-
ute, compact, or prior apportionment controls.  This Court 
has never before held that an interstate aquifer is subject 
to equitable apportionment, so Mississippi’s suit implicated 
a question of first impression.

The Court of Appeals, affirming the District Court, held
that interstate aquifers are comparable to interstate rivers 
and  are  thus  subject  to  equitable  apportionment.    It  rea-
soned that an aquifer “flows, if slowly.”  Hood ex rel. Miss., 
570  F. 3d,  at  630.    And  it  said  the  fact  that  an  aquifer  is
“located underground, as opposed to resting above ground,” 
was  of  “no  analytical  significance.”    Ibid.   Because  deter-
mining “Mississippi and Tennessee’s relative rights to the 
Aquifer” brought the case within the equitable apportion-
ment  doctrine,  the  Court  of  Appeals  affirmed  the  District
Court’s holding that Tennessee was an indispensable party. 
Id., at 630–631; see also Fed. Rule Civ. Proc. 19(a).  Joinder 
of Tennessee in the lower federal courts was not possible, 
however, because this Court has exclusive jurisdiction over
suits  between  States.  See  U. S.  Const.,  Art.  III,  §2;  28 
U. S. C. §1251(a).  So the Fifth Circuit held that the District 
Court had properly dismissed the suit.  Hood ex rel. Miss., 
570 F. 3d, at 632–633; Fed. Rule Civ. Proc. 19(b).

Mississippi then petitioned for a writ of certiorari.  It also 
sought leave to file a bill of complaint against Tennessee,
Memphis, and MLGW under our original jurisdiction.  The 
proposed complaint requested over $1 billion in damages for 
the  alleged  taking  of  Mississippi’s  water.    In  the  alterna-
tive, it sought equitable apportionment of the aquifer, with
a damages award for past diversions of groundwater.  We