page_title: San Juan Creek
section_title: Ecology
hierarchical_section_title: San Juan Creek / Ecology
caption_attribution_description: Drawing of ocean phase Steelhead (Oncorhynchus mykiss) from a pamphlet about the Lake Washington Ship Canal Fish Ladder at the Hiram M. Chittenden Locks, Seattle, Washington, scanned at 600 dpi and cleaned up.
context_page_description: San Juan Creek, also called the San Juan River, is a 29-mile long stream in Orange County, California, draining a watershed of 133.9 square miles. Its mainstem begins in the southern Santa Ana Mountains in the Cleveland National Forest. It winds west and south through San Juan Canyon, and is joined by Arroyo Trabuco as it passes through San Juan Capistrano. It flows into the Pacific Ocean at Doheny State Beach. San Juan Canyon provides a major part of the route for California State Route 74.
  Before Spanish colonization in the 1770s, the San Juan Creek watershed was inhabited by the Acjachemen or Juañeno Native Americans. The Juañeno were named by Spanish missionaries who built Mission San Juan Capistrano on the banks of a stream they named San Juan Creek. The watershed was used mainly for agriculture and ranching until the 1950s when residential suburban development began on a large scale. Since then, the human population has continued to encroach on floodplains of local streams. Flooding in the 20th and 21st centuries has caused considerable property damage in the San Juan watershed.
context_section_description: San Juan Creek was originally rich in riparian zones and other types habitat in both its upper and lower watershed, with wetlands totaling over 300 acres (1.2 km²) historically in the lower reaches, before urban development began in the 1950s. Only 0.3 percent of those wetlands remain. Recent efforts of stream conservation have been in the planning stage including habitat conservation plan work.
  There are sixteen prominent vegetation zones in the San Juan watershed, which include riparian vegetation, montane woodlands, coastal sage scrub and chaparral. Riparian vegetation is found along the banks of free-flowing streams with a measurable flow for at least several months out of the year. These include most of San Juan Creek, upper Arroyo Trabuco, Cañada Gobernadora, Bell Canyon, and other headwater streams, as well as scattered patches along Oso and El Horno creeks. Forests are present at high elevations, and also occur in close proximity to waterways. Coastal sage scrub is found on south-facing hillsides, while chaparral is found on higher-elevation hillsides and mesas. There are also a number of rare plant communities along rock outcroppings and vernal pools. However, introduced plant species, such as giant reed, castor bean, and tobacco tree, are rapidly spreading along streams. Giant reed has taken over huge areas of wetlands, swamps and riparian zones along the creek and its tributaries, although in recent years the county has taken steps toward eradicating it from San Juan Creek and other nearby streams.
  Historically, the San Juan watershed supported up to 12 invertebrate species, 5 fish species, 12 amphibian species, 35 reptile species, 143 bird species, and 42 mammal species, which benefited from the diverse vegetation communities present. Some streams and ponds host federally listed endangered/threatened species such as tidewater goby, fairy shrimp, and California red-legged frog. Federally listed bird species include least Bell's vireo, California gnatcatcher, California least tern, and southwestern willow flycatcher. Other listed species include Pacific pocket mouse and Quino checkerspot butterfly. As urbanization continues to increase in the San Juan watershed, most sensitive species have been pushed back to the foothills, mountains, and agricultural/ranching areas of the watershed.
  In 1987, just five bird species were confirmed in the watershed, while for fish, benthic invertebrates, and certain insects there were no confirmed observations, in part due to insufficient site coverage.
  Historic accounts suggest that San Juan Creek provided habitat for steelhead trout (Oncorhynchus mykiss irideus) in many historic accounts. However, pollution and competition from introduced sport fishes such as bluegill and striped bass have extirpated steelhead in the creek. Bacteria levels in San Juan Creek exceed state standards by 93 percent. The loss of riparian habitat along the lower 2.7 miles (4.3 km) of San Juan Creek and much of Trabuco and Oso Creeks due to channelization has also reduced steelhead habitat. However, in 2003 the California Department of Fish and Game reported three sightings of steelhead in a large stream pool along Trabuco Creek, immediately downstream of a drop structure that channels the creek beneath Interstate 5. In response, the Department of Fish and Game lobbied Caltrans to build a fish ladder at the structure, but it has not yet been implemented, due to concerns about structural stability of the I-5 bridge and the presence of a nearby natural gas pipeline.
caption: Steelhead trout have recently begun to return to San Juan Creek, only to find many man-made obstructions preventing them from spawning.
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