San Elijo Lagoon is a protected coastal wetland in northern San Diego County and one of the county’s largest remaining estuaries, shaped by both Escondido Creek and Pacific tides. Native people used its shores for thousands of years, and the Kumeyaay later moved through it seasonally. After Spanish naming in 1769 and later nearby ranching and farming, human alterations intensified with dikes, levees, and transportation berms that restricted tidal exchange. Despite those changes, the reserve still supports diverse habitats and hundreds of plant and animal species. Today it is managed through restoration, monitoring, invasive plant removal, and seasonal reopening of its lagoon mouth to sustain ecological health.