Colorado Asks Supreme Court to Reject Nebraska's South Platte River Water Challenge
Governor Jared Polis and Attorney General Phil Weiser urged the U.S. Supreme Court October 15 to dismiss Nebraska's lawsuit concerning the South Platte River Compact and the Perkins County Canal, arguing Colorado complies with its obligations and Nebraska has failed to demonstrate any justiciable dispute.
Nebraska appears to be leveraging the prospect of the canal and Supreme Court action to renegotiate the century-old compact rather than addressing specific violations, according to a brief filed by Colorado officials. The South Platte River originates in Colorado's Rocky Mountains and flows approximately 380 miles northeast into Nebraska, supplying water to some of Colorado's largest cities and most productive agricultural lands.
The river system serves as the dominant surface water source for Larimer and Weld counties, which together divert between 220,000 and 300,000 acre-feet annually from the South Platte and its associated ditch systems for municipal and agricultural uses. Weld County draws more than 80 percent of its agricultural irrigation and significant municipal supply from the river, while Larimer County obtains 50 to 60 percent of its total water from the South Platte system, supplemented by Colorado-Big Thompson Project imports.
Compact Grants Colorado Priority During Growing Season
The South Platte River Compact, signed in 1923 and ratified by Congress in 1926, establishes water rights between the two states with explicit provisions protecting Colorado diversions during irrigation season from April 1 to October 15.
Under the compact's terms, Nebraska expressly waived any right to South Platte River water in Colorado that would interfere with present or future Colorado diversions during the growing season. Nebraska may only divert surplus waters that flow past the state line after supplying all present and future Colorado diversions during that period.
"Water is the lifeblood of our state. We have always faithfully honored the century-old South Platte Compact and all other water agreements with our downstream neighbor states, and we will continue to do so," Polis said. "We refuse to sit idly by while Nebraska chases a meritless lawsuit that threatens Colorado's precious water resources, our robust agriculture industry, and our rural communities in Northeastern Colorado."
Colorado administers South Platte River water through the prior appropriation doctrine, where users with older water rights have allocations fulfilled before newer rights, particularly during shortages. The Colorado Division of Water Resources performs daily decisions on water distribution based on the priority system and compact obligations.
Nebraska Canal Project Dormant Since 1920s
Nebraska has failed to advance the Perkins County Canal for over 100 years despite the compact explicitly acknowledging the state's right to construct the project. Nebraska officials recently took preliminary steps to plan and permit the canal through the U.S. Army Corps of Engineers, but numerous procedural steps remain before identifying potential issues and studying impacts.
The canal concept originated in the early 1900s following the compact's signing. Nebraska conducted preliminary site investigations and preparatory work in the 1910s and 1920s but never built the project due to technical challenges, funding difficulties, engineering obstacles related to the Ogallala formation, and sufficient historic flows from Colorado.
Nebraska revived the canal plan in 2022 and established state laws with appropriated funds to begin planning and permitting. As of October 2025, the project remains in the feasibility and early environmental review phase, with no Clean Water Act Section 404 permit issued and no detailed engineering plans filed.
State Officials Defend Colorado's Compliance Record
Attorney General Weiser said Colorado complies with compact requirements and does not interfere with Nebraska's canal construction efforts, making the case premature for Supreme Court review. Future legal issues can be addressed through federal permitting processes or lower courts.
"Nebraska's claimed violations rely on speculative and premature allegations. To the extent any legal issues arise in the future, there are alternative forums to resolve them," Weiser said. "Even if the court decides to take up part or all of Nebraska's case, I'm confident that we will win on the merits. Both the facts and the law are on our side."
Jason Ullmann, State Engineer and Director of the Division of Water Resources, said Nebraska only recently suggested concerns about Colorado meeting compact obligations during irrigation season despite over 100 years of successful interstate cooperation.
"For over 100 years the Colorado State Engineer's Office has worked with Nebraska and performed the hard work of ensuring Colorado meets its compact obligations on the South Platte River," Ullmann said. "We were surprised and disappointed by Nebraska's lawsuit and are hopeful once all the briefs are filed that we can resume discussions to meet the mutual needs of both of our States."
Northern Colorado Communities Face Potential Water Supply Impacts
Communities throughout Larimer and Weld counties depend heavily on South Platte River system water for municipal and agricultural uses. Weld County, Colorado's most productive agricultural county, relies on the river for tens of thousands of acres of irrigated corn, wheat, sugar beets, alfalfa and livestock feed.
Greeley, with a population near 110,000, draws most of its municipal supply from the South Platte and related ditches. Other affected municipalities include Evans, Windsor, Eaton, Severance, Milliken, Johnstown, Fort Lupton and Platteville in Weld County, along with Fort Collins, Loveland, Berthoud and Timnath in Larimer County.
Large irrigation companies including Greeley-Loveland, New Cache la Poudre, and Larimer & Weld Company deliver South Platte water to agricultural operations throughout both counties. Combined farming and ranching operations in the two counties encompass nearly 3 million acres and generate over $2.2 billion in annual agricultural production value, according to the U.S. Department of Agriculture.
If Nebraska succeeded in altering compact water allocations, upstream Colorado users would see reduced available supplies, particularly affecting junior water rights holders, smaller irrigation companies and growing municipalities dependent on purchased or transferred irrigation rights.
The Supreme Court has original and exclusive jurisdiction over interstate disputes including water rights. States must file a motion for leave to file a bill of complaint to bring cases before the court.
The Supreme Court must still decide whether to accept the case, designated Nebraska v. Colorado, case number 220161.
Colorado's Response in Opposition to Nebraska's Motion for Leave to File Bill of Complaint is available through the state Attorney General's office.