Updated 07/28/2021: The Salton Sea—a lake located in Southern California—is the largest inland water body in the state. The sea has few natural inlets of water, has no natural outlets, and is largely sustained by agricultural runoff from farmlands in the Imperial and Coachella Valleys. In recent decades, agricultural runoff to the Salton Sea has diminished due to decreasing agricultural inflows , evaporation, and reduced precipitation, causing the sea to shrink and increase in salinity. High salinity levels, combined with greater concentrations of nutrients and toxins , have altered the sea’s ecosystem and surrounding habitat, making it difficult for most fish and bird species to survive. The Salton Sea’s diminishing size also has exposed lake bed (i.e., playa) around the sea’s shoreline; this playa contains toxic substances that may circulate in the air and impair local and regional air quality. Over time, federal, state, and private entities have developed proposals to manage and restore parts of the Salton Sea. These efforts have common objectives, including controlling salinity, maintaining some of the sea’s habitat, and stabilizing sea water levels. The current and most prominent restoration initiative, the Salton Sea Management Program (SSMP), was releas ed by the State of California in 2017. The SSMP’s first phase is being implemented from 2018 to 2028. The initiative includes activities to convey water to the Salton Sea, reduce salinity in the sea, and restore approximately 30,000 acres of exposed playa. Phase 1 is estimated to cost $420 million. Some federal agencies, such as the Bureau of Reclamation (part of the Department of the Interior), are collaborating with the State of California to implement the SSMP. The federal role in restoring the Salton Sea is limited to a handful of projects that address issues on lands in and around the sea managed by federal agencies such as the U.S. Fish and Wildlife Service, the Bureau of Reclamation, the Bureau of Land Management, and the Department of Defense. Unlike in areas such as Lake Tahoe, the Everglades, and the Chesapeake Bay, Congress has not authorized a comprehensive program to restore the Salton Sea. The scope and content of plans to restore the Salton Sea have generated debate, and legislation to provide additional federal support for restoration has been introduced in the 117th Congress. Many stakeholders support restoring the Salton Sea because of the sea’s ecological significance as a large wetland along the Pacific Flyway, its role in providing habitat for fish and wildlife, and its economic importance to the region. Some also argue that restoration might mitigate the effects of increasing playa exposure, which is linked to regional airborne pollution. Some observers contend the sea should not be restored; they argue that the area’s geological history demonstrates a pattern of water bodies naturally shrinking, disappearing, and reforming over time and assert that the Salton Sea is following a similar process. Congress may consider issues related to restoring the Salton Sea, including the nature and extent of federal involvement in restoration; how (or if) the federal government should collaborate with the State of California in restoration efforts under the SSMP; and what (if any) federal responsibilities exist for mitigation of airborne toxins that occur due to exposed playa on federal lands. Congressional Research Service R46625.