For migratory waterbirds, the availability and quality of suitable stopover habitat can affect body condition and demographic parameters throughout the annual cycle. This study investigates the importance of the Salton Sea, a large saline lake located in the southwestern United States near the USA-Mexico border, for migrating Caspian Terns (Hydroprogne caspia) fitted with long-duration satellite telemetry tags in the northwest contiguous USA. During fall migration, 100% (n = 25) in 2014 and 98% (n = 63) in 2015 of all tagged individuals were tracked to the Salton Sea, with median durations of stay lasting 36 and 25 days, respectively. Use of the Salton Sea during subsequent spring migrations was less consistent than in fall, but still substantial, with 91% (n = 23) and 68% (n = 53) of all birds conducting brief stops there during 2015 and 2016, respectively. The future of the Salton Sea as suitable habitat for fish and piscivorous birds is uncertain due to rising salinity levels caused by reduced input flows. It is also uncertain if other wetlands in the region can serve as replacement habitat for Caspian Terns and other migratory piscivorous species should the Salton Sea cease to provide fish prey.