In early November, the U.S. Supreme Court agreed to hear a case brought by the Navajo Nation that could have far-reaching impacts on tribal water rights in the Colorado River Basin. In its suit, the Navajo Nation argues that the Department of Interior has a responsibility, grounded in treaty law, to protect its future access to water from the Colorado River. Several states and water districts have filed petitions opposing the Navajo Nation, stating that the river is “already fully allocated.” The case highlights a growing tension in the region: As water levels fall and states face cuts and a two-decade-long megadrought, tribes are working to ensure their water rights are fully recognized and accessible...