RENO, Nev. (AP) – A federal appeals court has upheld most of a ruling that ordered a rural Nevada irrigation district to pay back billions of gallons of water that it took from a tribe decades ago.

The 9th U.S. Circuit Court of Appeals on Tuesday directed a federal judge in Reno to go back and determine how much more water the Pyramid Lake Paiutes are entitled to as a result of the Truckee-Carson Irrigation District illegally diverting flows for its own farmers and ranchers in northern Nevada's high desert during the 1970s and 1980s.

The appellate court rejected most of the district's bid to overturn a 2003 decision that determined the water from Lake Tahoe and other reservoirs should have continued down the Truckee River to help bolster a traditional tribal fishery in serious decline.

U.S. District Court Judge Howard McKibben in Reno was correct when he determined at that time the irrigation district had “willfully failed to comply” with a 1973 agreement that divided up the water, according to the opinion Judge Mary Schroeder issued on behalf of a three-judge panel of the 9th Circuit in San Francisco.

Since then, the district has made “several additional attempts to sidestep accountability” under that agreement, she wrote.

A lawyer for the tribe who hailed the ruling as a victory said Wednesday that he is certain it will mean additional water for the tribe and perhaps as much as 75 percent more than McKibben ordered in 2003.

“The district had been thumbing its nose at the 9th Circuit, and the 9th Circuit really put its foot down and said, `You have no business doing this, and you have to pay it back,”' said Don Springmeyer, a Las Vegas attorney representing the Paiutes.

“The district wanted to get Judge McKibben's ruling tossed out and exactly the opposite happened. The court said in fact there is going to be more,” he told The Associated Press.

Michael Van Zandt, a San Francisco lawyer representing the district based in Fallon about 60 miles east of Reno, said he disagrees with many of the appellate court's conclusions.

He said the district has not decided whether to ask for a rehearing before the full 9th Circuit or to make their arguments again before McKibben.

McKibben ruled in 2003 that the district had illegally diverted 200,000 acre feet of water that should have gone to the tribe from 1974-84. That's enough water to cover 200,000 acres or 312 square miles of one-foot-deep water – a total of about 65 billion gallons.

The tribe originally sought to recoup 1 million acre feet of water.

The new ruling from the 9th Circuit directed McKibben to review the calculations used to estimate the amount of water that flowed over spillways in some years, as well as the margin of error in calculating inaccurate readings on gauges used to measure flows from irrigation canals.

Springmeyer said alterations in those calculations suggested by the appellate court could result in an additional 150,000 acre feet being added to McKibben's original order.

“TCID is now going to have to have quite an interesting discussion among themselves about how to pay this 350,000 acre feet back,” he said.

The legal battle began, which has roots dating back to the early 1900s, centers on the fact that more water rights have been appropriated along the Truckee and Carson rivers than the amount of water in those rivers.

As a result, Pyramid Lake has been declining for generations while farmers in the irrigation district east of Reno complain they aren't getting enough water. Between 2,500 and 3,000 members of the irrigation district currently rely on the water for their crops and livestock.

Van Zandt said if the 9th Circuit ruling stands, he would “expect some kind of upward adjustment” in the amount of additional water ordered to the tribe but he didn't know how much.

He said he was glad the 9th Circuit sided with TCID in questioning the legal basis for McKibben's order that the district pay any back interest owed in the form of water rather than money. The 9th Circuit said it was vacating that part of the judge's order, at least until he explains his reasoning in his next decision.