Tijunana River Nation Estuary The Tijuana River Estuary is an inter-tidal coastal wetland at the mouth of the Tijuana River in San Diego County, California, in the United States bordering Tijuana, Baja California, Mexico. It is the location of the Tijuana River National Estuarine Research Reserve, Tijuana Slough National Wildlife Refuge, and Border Field State Park. The estuary is a shallow water habitat. Index of ... Border Field State Park Tijuana River Estuary