Oklahoma won a major victory Thursday in defense of the state's water supply, as the U.S. Supreme Court ruled unanimously that Texas can't reach across the border to claim a share of the Kiamichi River.

Oklahoma Attorney General Scott Pruitt said the decision protected Oklahoma's right to manage its water for generations to come, though the state is still in negotiations with the Chickasaw and Choctaw tribes about water rights in southeastern Oklahoma.

The high court's decision ended a six-year legal battle with the Tarrant Regional Water District, a Texas state agency that claimed a water compact among Texas, Oklahoma, Arkansas and Louisiana gave Texas the right to reach into Oklahoma to get its share of allotted water.

The Red River Compact — approved by Congress in 1980 — gives each of the four states an equal share of excess water from the Kiamichi River. But the compact doesn't explicitly say whether one state can cross a border without permission to get its share.