San Juan Creek

San Juan Creek, also called the San Juan River, is a 29-mile (47 km) stream in Orange County, California that consists of a catchment basin encompassing 133.9 square miles (347 km2). Its mainstem rises in the Santa Ana Mountains, in the Trabuco Ranger District of the Cleveland National Forest. From there it runs parallel to the Ortega Highway as it winds west and south through San Juan Canyon, where it is joined by numerous small tributaries, and is joined by Trabuco Creek, its main branch as it passes through San Juan Capistrano. It flows into the Pacific Ocean at Doheny State Beach. Once out of the foothills, San Juan Creek flows through the city of San Juan Capistrano where groundwater flow direction generally is from the northeast to the southwest. Groundwater in this basin at the San Juan Capistrano reach is considered good. Recent efforts of stream conservation have been in the planning stage including habitat conservation plan work.

Historically, the San Juan Creek watershed was inhabited by the Acjachemen, now Juañeno Indians. The Juañeno received their current name from Spanish conquistadors in the 1770s, who built Mission San Juan Capistrano very near San Juan Creek, giving it its name. After the Spanish settlement, development in the watershed continued to grow and pollution of the creek has increased. The construction of Dana Point Harbor in 1960 increased the pollution of San Juan Creek at its mouth, posing an increasing danger to visitors of Doheny State Beach. In the late 1990s and early 21st century, floods destroyed many river control structures in the San Juan watershed, and the risk of floods continues to grow.

Although the San Juan watershed was formerly rich in biodiversity, with sixteen major plant communities and hundreds of species of birds, invertebrates, mammals, and others, the watershed is projected to be 48 percent developed by the year 2050. Many reaches of open land in the San Juan watershed are now heavily developed, and urban runoff coming from residential communities is taking an increased toll on the creek and its tributaries. Although the mainstem San Juan Creek does not have any water diversions or dams, its tributaries are heavily affected, most notably Trabuco and Oso Creeks.