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Big Horn 1 (1988) and Big Horn 2 (1992) [**]

Situation: In the 1970s and 1980s many western states began formal proceedings to determine who had rights to how much water within their borders. Demand for water was growing, as new residents flooded into the region, Indian tribes became more assertive of their rights, and environmentalists sought consideration for the needs of fish and forests. Tribal claims in particular created uncertainty because, even though the tribes weren't using as much water as they were likely entitled to, under the "reserved" or "Winters" rights doctrine their claims almost always had priority over those of other users. Non-tribal users feared that under "first in time, first in right" rules, they might have to start giving back water they had been using to support irrigation, mining, or urban growth.

Wyoming began its adjudication process in 1977. The legislature first passed enabling legislation, then the state filed suit against the tribes of the Wind River Indian Reservation and some 20,000 other water rights holders in the Big Horn river basin. A special master was appointed to oversee the adjudication in 1979, and after he reported his findings in 1982, the case began winding its way through various courts.

Decision: The Wyoming Supreme Court handed down two major decisions in this case. In the first, known as Big Horn 1 (1988), the court decided that: 1) the Wind River tribes did indeed have reserved water rights that preceded all other state users, and 2) since the original purpose of the reservation was to support agriculture, the amount of water reserved should be based on the "practicably irrigable acreage" standard established in Arizona v. California. In Big Horn 2 (1992), the court decided that the tribes could not convert their water use from irrigation to instream flow without first following state procedures. Wyoming state law says that only the state of Wyoming owns an instream flow right. So the court's decision in essence told the tribes: If you want to use your water for instream flow you, like any other Wyoming user, will have to "buy" that right from the state.

Implications: The "practicably irrigable acreage" (PIA) standard the Wyoming Supreme Court used in Big Horn 1 is controversial, to say the least. Under this standard, experts gather data on soil characteristics, hydrology, economics, and engineering in order to figure out how much reservation land can be "practicably irrigated." This means that the amount of water in a reserved right is not based on how much water a tribe used for irrigation in the past or how much water it's using now. Rather, it's based on how much could be used if all the "practicably irrigable acreage" were in fact being irrigated. The US Supreme Court was offered a chance to overrule this standard when the Big Horn 1 case came to it on appeal in 1989. But a tie vote (Justice O'Connor abstained) left the Wyoming decision, and the PIA standard, in place. Thus in states like Idaho, the tribes hold potentially large claims against state water, in this case from the Snake River.

[**] The formal title is: In re: The GENERAL ADJUDICATION OF ALL RIGHTS TO USE WATER IN THE BIG HORN RIVER SYSTEM and all other sources, State of Wyoming.

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