Nebraska officials on Wednesday announced a lawsuit against Colorado, alleging that the Centennial State is allowing “unlawful water diversions” from a transboundary resource.

Nebraska Gov. Jim Pillen (R) and Attorney General Mike Hilgers accuse Colorado of threatening Nebraska’s water supply along the South Platte River in multiple ways.

The lawsuit alleges that Colorado has “deprived” Nebraskans of their water rights during irrigation season, while also “obstructing” plans to construct a long-disputed conduit called the Perkins County Canal.

“Nebraska must push forward to secure our water for future generations,” Pillen said in a statement, noting that his state had “made every reasonable effort to resolve our differences with Colorado.”

The complaint in large part revolves around the enforcement of the South Platte River Compact, a deal signed by the states in 1923. The agreement limits Colorado’s usage of the river and defines how much water Nebraska can receive during the summer irrigation season and the winter non-irrigation season.

The headwaters of the South Platte River are located southwest of Denver near South Park, from which it generally heads northeast through central Denver and the metropolitan region, to Fort Lipton and across the Colorado Eastern Plains, before heading into Nebraska.

Because the U.S. Supreme Court has original jurisdiction regarding disputes between the two states, the Nebraska officials argued that the court’s input is required to resolve a now irreconcilable dispute.

“Today’s action will ensure that Nebraska receives all the water to which it is entitled to under the Compact and that Nebraska’s agriculture and economy are protected,” Hilgers said in a statement.

“Water is the essential lifeblood of Nebraska’s economy, and it’s my goal to protect one of the state’s most important assets,” the attorney general added.

The lawsuit maintains that the 1923 compact requires Colorado to disconnect certain water users whenever Nebraska is not receiving 120 cubic feet per second of flow during the irrigation season.

Currently, the complaint argues, Colorado enables users with “junior” water rights statuses to take Nebraska’s share of summertime water violating the agreement and Nebraska’s “senior” rights status.

The rights in question stem from a historic U.S. West system that adheres to a “first in time, first in right” approach to water access. This method, rooted in the mid-19th century homesteading and gold rush era, enabled farmers and miners to secure and divert water according to their arrival, rather than their geographical position along the river.

The 1923 compact, per the lawsuit, also permits Nebraska to divert 500 cubic feet per second of water flow in the winter, as well as additional water when the Perkins County Canal is constructed.

As it stands today, Colorado pumps water in the winter and gradually releases it into the river to compensate for summer overuse, the complaint explains. While this occurs under the theory that the water reaches Nebraska by the following irrigation season, the lawsuit criticizes this method for taking water from the state when farmers are in greatest need.

To guarantee that Nebraska can fulfill its rights in the winter and regulate water flow, the state has set out to build the Perkins County Canal, the document explains.

The Nebraska state legislature in 2023 approved $574.5 million in funding for the canal’s constructions despite pushback from lawmakers who had sought to reduce the cost.

While recognizing that Colorado has acknowledged its neighbor’s entitlement to build the canal, the Nebraska officials expressed frustrations that negotiations over the project’s fine print have persisted for years and ultimately reached a stalemate.

“Despite Nebraska’s good faith efforts, Colorado won’t agree on such basic things as the location or the size of the Canal, or how much water can flow through it,” a fact sheet issued by the attorney general argued.

In response to the lawsuit, Colorado Gov. Jared Polis’s (D) office issued a press release that described the complaint as “meritless.”

“I am disappointed that the states of Colorado and Nebraska will need to waste time and money in court over this meritless challenge,” Polis said.

The governor stressed that Colorado has always complied with the South Platte Compact and has met “in good faith” with Nebraska officials, despite “attempts to intimidate Colorado landowners.”

“This escalation by Nebraska is needless, and Colorado will take all steps necessary to aggressively defend Colorado water users, landowners, and our rural economy,” Polis added.

Colorado Attorney General Phil Weiser echoed these sentiments in his own statement, slamming neighboring leaders for prioritizing politics over agricultural and likely setting in motion “decades of litigation.”

Describing the Perkins County Canal project as “wasteful,” he said that the canal’s operation would require Colorado to build new water infrastructure to offset the impacts of Nebraska’s initiative.

“When the dust finally settles, likely over a billion dollars will have been spent—tens of millions of that on litigation alone and no one in Nebraska or Colorado will be better off,” Weiser added.