The Red River Compact is a congressionally sanctioned agreement that allocates water rights within the Red River basin among the states of Oklahoma, Texas, Arkansas and Louisiana.
The area it governs is divided into five subdivisions called "reaches," each of which is further divided into smaller "subbasins," Thursday's opinion said.
The case deals with rights under the compact to water located in Oklahoma's portion of Reach II, subbasin 5. In Reach II, the compact -- "recognizing that Louisiana lacks suitable reservoir sites to store water during high flow periods and that the upstream states [Texas, Oklahoma and Arkansas] were unwilling to release their own stored water for the benefit of a downstream state -- granted control over the water in four upstream subbasins to the states in which each is located and required that water in a fifth subbasin, subbasin 5, be allowed to flow to Louisiana at certain minimum levels.
The Tarrant Regional Water District in north-central Texas unsuccessfully tried to buy water from Oklahoma and others. Knowing that the Oklahoma Water Resources Board would likely deny permission to take water from that state's borders, Tarrant filed suit in federal court simultaneously with its permit application.
The suit sought an injunction against the Oklahoma board's enforcement of state water statutes, saying they were pre-empted by federal law in the form of the compact.
A federal judge ruled for the Oklahoma board, and a federal appeals court affirmed. The Supreme Court affirmed the appeals court ruling.
The opinion written by Justice Sonia Sotomayor said: "The compact does not pre-empt the Oklahoma water statutes. ... Three things persuade the [Supreme] Court that the compact did not grant cross-border rights: the well-established principle that states do not easily cede their sovereign powers; the fact that other interstate water compacts have treated cross-border rights explicitly; and the parties' course of dealing" -- how they negotiated rights."