The U.S. Supreme Court will weigh in on a legal battle over one of Colorado’s critical water sources as a neighboring state seeks to use more water from the South Platte River.

The nation’s highest court on Monday announced it would hear the case, in which Nebraska officials claim Colorado water administrators are violating a century-old water compact by failing to send enough of the river’s water across the border. They also say Colorado officials are interfering in the neighboring state’s efforts to build a canal that would allow it to take more of the river’s water.

Colorado Attorney General Phil Weiser on Monday denied Nebraska officials’ allegations that the Centennial State was violating the 1923 South Platte River Compact.

“Colorado is complying with the South Platte River Compact and not interfering with Nebraska’s efforts to build the Perkins County Canal,” Weiser said in a statement. “Today’s court decision merely opens the door for Nebraska to bring its claims against Colorado. Nebraska’s burden to prove those claims is incredibly high and we will vigorously defend Colorado’s full entitlements under the compact.”

The South Platte River is a critical water source for Front Range cities and Eastern Plains agriculture. The river originates in the Front Range mountains before flowing through Denver and cutting across the northeast portion of the state and into Nebraska.

More than 85% of the state’s population lives in the river basin, and the river irrigates more than 850,000 acres of farmland — the highest concentration of irrigated acres of any river basin in Colorado. The South Platte provides, on average, half of the annual supply for Denver Water, which serves 1.5 million people across metro Denver, according to the utility.

The South Platte River Compact allows Nebraska to use more of the river’s water during the winter, but only if it builds a canal system. Nebraska leaders in 2022 revived long-dormant plans to build the Perkins County Canal, a move that could require them to use eminent domain to obtain land in Colorado.

Farmers in northeastern Colorado say that, if built, the canal would dry up tens of thousands of acres of farmland and threaten the economies of the corner of the state.

Nebraska officials last year surprised Colorado leaders by taking their allegations to the Supreme Court. The two states had been meeting for months to discuss the proposed canal project.

The Supreme Court asked the Office of the Solicitor General to weigh in on whether it should take the case. In May, the federal office — tasked with representing federal interests at the Supreme Court — argued that the court should decide Nebraska’s claim that Colorado is not sending enough water over the state border, but deny consideration of Nebraska’s other issues.

Controversy over compact-obligated water deliveries between two states is a “quintessential” Supreme Court question, the brief states. The solicitor general’s office suggested appointing a special master — a subject-matter expert outside of the nine justices — to handle the issue.

The solicitor general’s brief argues that the Supreme Court should not hear Nebraska’s arguments that Colorado is obstructing its efforts to build the Perkins County Canal because, the office said, Nebraska has not identified any actions by Colorado officials that have substantially interfered in the project. Other potential canal-related problems identified by Nebraska are hypothetical, the solicitor general said, as the state has just begun the permitting process and, therefore, is not ready for Supreme Court consideration.

It’s unclear which issues the Supreme Court will consider as it hears the case. The order Monday allows Nebraska to file its complaint against Colorado.

In its brief to the court, the Colorado Attorney General’s Office called Nebraska’s compact violation claims a “hunch.” Weiser previously said he doubted the Supreme Court would take the case.

Colorado’s attorneys now have 30 days to respond to Nebraska’s complaint. Litigation could span years, attorneys for both states have said.

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