The Tijuana River is a river that flows from the Sierra de Juárez mountains in Mexico into the Pacific Ocean, near San Diego, California. It serves as a natural border between the two countries and is approximately 120 miles long. The river's watershed covers an area of about 1,700 square miles, supporting various ecosystems along its banks. The river is significant for both environmental and cultural reasons. It provides habitat for wildlife, including migratory birds, and is part of the Tijuana River National Estuarine Research Reserve. However, it also faces challenges such as pollution and habitat degradation, impacting the surrounding communities and ecosystems.