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On June 29, 2026, the Supreme Court of the United States granted Nebraska’s motion requesting the Court’s permission to file a bill of complaint against Colorado for alleged violations of the South Platte River Compact. This alert provides an overview of the South Platte River Compact, Nebraska’s claims against Colorado, and what lies ahead.
The legal mechanism for Colorado and Nebraska to divide up the water of the South Platte River arises in the “Compact Clause,” Article I, Section 10, Clause 3 of the United States (U.S.) Constitution. Interstate compacts are valid upon approval of Congress and the compacting states’ legislatures, and function legally as both contracts and statutes. See Kansas v. Nebraska, 574 U.S. 445, 477 (2015). The first compact to apportion the waters of an interstate stream was the Colorado River Compact, which was signed by the seven basin states in November 1922, and approved by Congress in 1928.
The Supreme Court is authorized to consider disputes between compacting states under its “original” jurisdiction authority found in Article III, Section 2, Clause 2 of the U.S. Constitution and 28 U.S.C. § 1251(a). This authority is distinct from the Supreme Court’s “appellate” jurisdiction authority found in the same constitutional clause and 28 U.S.C. §§ 1253-60, which authorize the Supreme Court to consider petitions for certiorari to review a lower court’s decision. Under its original jurisdiction authority, the Court sits as a trial court and a state must move the Court for leave to file a bill of complaint. Among the Court’s considerations to take a case are “the nature of the interest of the complaining State,” focusing on the “seriousness and dignity of the claim.” South Carolina v. North Carolina, 558 U.S. 256, 277 (2010). While the Court historically conducted trials between states, see Wyoming v. Colorado, 259 U.S. 419, 455 (1922), for over 100 years the Court has referred original actions to “special masters” to sit as fact finders.
Signed in April 1923 and approved by Congress in 1926, the South Platte River Compact (Compact) apportions the waters of the river between Colorado and Nebraska. The Compact divides the river into an “Upper Section” (upstream of the western boundary of Washington County, Colorado) and “Lower Section” (between said boundary and the state line) and the year into the irrigation season (April 1 to October 15) and non-irrigation season (October 15 to April 1).
Source: https://dnr.colorado.gov/sites/dnr/files/documents/South%20Platte%20Overview%20 Map%20%281%29.pdf.
Three articles of the Compact are relevant here. First, Article IV provides Nebraska a priority date of June 14, 1897, and, during the irrigation season, obligates Colorado to curtail diversions from junior users in the Lower Section that diminish the flow at the “Interstate Station” (near Julesburg, Colorado) below 120 cubic feet per second (cfs). Second, Article VI provides Nebraska the right to construct a canal (the “Perkins County Canal,” or “Canal”) near Ovid, Colorado, that, if built, would have a priority date of December 17, 1921, and, during the non-irrigation season, the right to divert flows reaching the Lower Section except those needed to meet senior rights and Colorado’s reserved 35,000 acre-foot (AF) storage right. Third, Article VIII obligates Colorado officials to deliver water to Nebraska “without necessity of enactment of special statutes for such purposes.”
On July 16, 2025, Nebraska filed a motion for leave to file a bill of complaint with the Court, thereby initiating Original Action No. 161. First, Nebraska alleged Colorado has allowed diversions to continue that should be curtailed when flows at the Interstate Station fall below 120 cfs, depriving Nebraska of up to 1,300,000 AF, in violation of Article IV. Second, Nebraska alleged Colorado has obstructed Nebraska’s efforts to construct the Canal and is preventing Nebraska from accessing water to which it would be entitled if the canal were in place, in violation of Article VI. Third, Nebraska alleged Colorado has created such a complex water administration scheme (which includes the approval of “augmentation plans” that allow out-of-priority diversions by junior users if they provide replacement water, which has enabled extensive groundwater development to occur) that it is no longer self-executing, in violation of Article VIII.
On October 15, 2025, Colorado filed a response in opposition to Nebraska’s motion. Colorado asked the Court to deny Nebraska’s leave to file a bill of complaint, arguing Colorado has not interfered with Nebraska’s construction of the Canal and Nebraska’s allegation that Colorado has breached its obligations to curtail Lower Section users during the irrigation season is not sufficiently developed; thus, the claims are unripe or otherwise not ready for the Court’s review.
On November 17, 2025, the Court invited the Solicitor General to file a brief expressing the views of the U.S. On May 20, 2026, the U.S. filed an amicus brief. The U.S. argued the Court should allow Nebraska to bring its Article IV claim because Nebraska’s allegations are sufficiently developed to show a causal link between Colorado’s non-curtailment and low river flows, and that the claim should be referred to a special master to develop facts. The U.S. also urged the Court to disallow the Article VI claim related to the not-yet-constructed Canal based on ripeness, and to disallow the Article VIII claim because Nebraska failed to state a claim.
On June 29, 2026, the Court granted the motion, accepting all three of Nebraska’s allegations.
While its claims against Colorado play out in court, Nebraska is moving forward with the Perkins County Canal Project. On February 13, 2026, Nebraska’s Department of Water, Energy, and Environment submitted a permit application for the discharge of dredged or fill material under Section 404 of the Clean Water Act to the United States Army Corps of Engineers. The Canal Project also includes two storage reservoirs of 17,000 AF and 77,000 AF.
As for the litigation schedule, the Court set a deadline of September 28, 2026, for Colorado to file an answer to Nebraska’s bill of complaint. In the meantime, many unresolved questions—such as the proper condemnation process for Nebraska to follow to acquire the property associated with the Canal Project within Colorado—await the Court’s review.
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