The San Pedro River is one of the last free flowing rivers in the West and an important habitat for many species. Congress recognized the ecological importance of the San Pedro River and expressly reserved water to protect, conserve, and enhance the riparian area—the San Pedro Riparian National Conservation Area (“SPRNCA”). The exact amount of water that Congress reserved is unquantified pending determination in Arizona’s Gila River General Stream Adjudication, a comprehensive adjudication, initiated in 1974, of all water claims in the Gila River watershed. Meanwhile, flows in the San Pedro River are strained by groundwater pumping in nearby communities in Cochise County. Cochise County has adopted a requirement that before any proposed housing development is approved, the Arizona Department of Water Resources (“ADWR”) must find that there is sufficient groundwater to support the proposed development. Yet the Arizona Supreme Court recently held that ADWR does not need to consider the water reserved for SPRNCA—while it remains unquantified—when determining whether there is sufficient groundwater for a proposed development. This is problematic because the water reserved for SPRNCA will probably not be quantified anytime soon and will continue to be threatened by an increasing population reliant on groundwater. Consequently, the state adjudication is insufficient to protect the water for SPRNCA, and the federal government should take an alternative approach to protect the reserved water for SPRNCA—that is, assert the water right in SPRNCA in federal district court.