Document ID: ./input/supremecourt_opinions/opinions/21pdf/143orig_1qm1.pdf
Page Number: 12

Cite as:  595 U. S. ____ (2021) 

9 

Opinion of the Court 

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 Missis-
sippi.  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 inter-
state 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 eq-
uitable apportionment. 

B 

Mississippi contends that it has sovereign ownership of 
all groundwater beneath its surface, so equitable apportion-
ment ought not apply.  We see things differently.  It is cer-
tainly  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  be-
tween  several  States,  each  one  “has  an  interest  which