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2 

ARIZONA v. NAVAJO NATION 

Opinion of the Court 

The  question  in  this  suit  concerns  “reserved  water
rights”—a  shorthand  for  the  water  rights  implicitly 
reserved  to  accomplish  the  purpose  of  the  reservation. 
Cappaert  v.  United  States,  426  U. S.  128,  138  (1976);  see 
also  Winters  v.  United  States,  207  U. S.  564,  576–577 
(1908).  The  Navajos’  claim  is  not  that  the  United  States 
has interfered with their water access.  Instead, the Navajos 
contend that the treaty requires the United States to take 
affirmative  steps  to  secure  water  for  the  Navajos—for 
example, by assessing the Tribe’s water needs, developing
a plan to secure the needed water, and potentially building
pipelines,  pumps,  wells,  or  other  water  infrastructure—
either to facilitate better access to water on the reservation 
or to transport off-reservation water onto the reservation. 
In  light  of  the  treaty’s  text  and  history,  we  conclude  that 
the treaty does not require the United States to take those 
affirmative  steps.  And  it  is  not  the  Judiciary’s  role  to
rewrite  and  update  this  155-year-old  treaty.    Rather, 
Congress  and  the  President  may  enact—and  often  have
enacted—laws to assist the citizens of the western United 
States, including the Navajos, with their water needs. 

I 

The  Navajo  Tribe  is  one  of  the  largest  in  the  United 
States, with more than 300,000 enrolled members, roughly 
170,000  of  whom  live  on  the  Navajo  Reservation.  The 
Navajo  Reservation  is  the  geographically  largest  in  the 
United States, spanning more than 17 million acres across
the States of Arizona, New Mexico, and Utah.  To put it in 
perspective,  the  Navajo  Reservation  is  about  the  size  of 
West Virginia.

Two treaties between the United States and the Navajo
Tribe led to the establishment of the Navajo Reservation. 
After the Mexican-American War ended in 1848, the United 
States  acquired  control  over  massive  new  territory 
throughout  what  is  now  the  western  United  States—