U.S. Supreme Court Allows Nebraska's Water Rights Lawsuit Against Colorado To Proceed

Highlights

• The U.S. Supreme Court has granted Nebraska's motion to file a complaint against Colorado for alleged violations of the South Platte River Compact.
• Nebraska alleges that Colorado has failed to protect its irrigation season rights under the Compact against more "junior" users and obstructed Nebraska's efforts to construct a canal to divert water for use during the non-irrigation season.

The U.S. Supreme Court has allowed Nebraska to proceed with filing a bill of complaint against Colorado, alleging violations of the South Platte River Compact between the two states. The Compact, which was ratified in 1926, governs each state's use of water from the South Platte River. The Supreme Court's ruling, issued on June 29, 2026, kicks off what is likely to be a long process of resolving water rights disputes between the neighboring states.

Background

Under the Compact, Colorado and Nebraska share water from the lower section of the river, which flows from Washington County, Colorado, to the border with Nebraska. The Compact requires that Colorado ensures that the flow of the river, as measured at an interstate flow station, does not fall below 120 cubic feet per second during the annual irrigation season between April 1 and October 15. Colorado is not required to ensure a minimum flow during the non-irrigation season. The Compact authorizes the construction of a canal by Nebraska from Colorado to divert water for use during the non-irrigation season.

Nebraska's Claims and Colorado's Response

In July 2025, Nebraska moved for permission to file a complaint against Colorado in the Supreme Court (which, under Article III, Section 2 of the U.S. Constitution, has original jurisdiction over claims between states) for allegedly failing to protect Nebraska's rights under the Compact and preventing Nebraska from constructing a canal. In the complaint, Nebraska alleges that Colorado has allowed its state's citizens with more "junior" claims to South Platte River water (i.e., claims that post-date Nebraska's) to divert more water than the Compact allows. Nebraska also alleges that Colorado has not cooperated and even hindered Nebraska's ability to build a canal, which Nebraska has taken steps to construct the past few years.

Colorado opposed Nebraska's motion to file, arguing that its claims were not ripe for review. In an amicus curiae brief filed on May 20, 2026, the U.S. government partially agreed, urging the Court not to allow Nebraska to file some of its claims but arguing that the Court should allow Nebraska to file a claim alleging that Colorado is denying the state water that it is entitled to under the Compact.

Implications

The Supreme Court's go-ahead for Nebraska to file its complaint kicks off what will be a long process toward resolving the water rights issues between it and Colorado. These types of disputes between states can typically take many years to resolve. The Court will likely appoint a special master to try to resolve the issues at first, but the timeline for that appointment and the special master to review the facts and issue recommendations is not known.

The dispute also highlights many of the issues that can plague interstate water compacts, such as the lengths to which states will go to maximize their use of water, disputes between upstream and downstream users, and the effects that long-running droughts in the American West have on ensuring adequate flow.