San Juan Creek originates in the Santa Ana Mountains of Orange County, California, flowing approximately 29 miles southwest before reaching the Pacific Ocean at Doheny State Beach in Dana Point. The watershed encompasses roughly 133 square miles, with headwaters beginning near the Cleveland National Forest boundary. The creek's upper reaches traverse steep, rugged terrain before transitioning to gentler gradients through San Juan Capistrano and the coastal plain.

The creek supports limited paddling opportunities, primarily restricted to the lower reaches during winter and early spring when flows are sufficient. Most of the year, San Juan Creek maintains minimal flow due to groundwater pumping, diversions, and the semi-arid climate. The estuary at Doheny State Beach occasionally offers brief kayaking conditions when the sandbar breaches and tidal influences extend upstream, though this remains highly seasonal and unpredictable.

Water quality challenges stem from urban runoff, particularly during storm events, when the creek carries significant sediment loads and pollutants from upstream development. The watershed has experienced substantial channelization in its lower sections, though portions of the upper watershed retain relatively natural conditions with perennial wetted pools providing important aquatic habitat.

Historically, San Juan Creek supported steelhead trout populations, with documented spawning runs into the 1940s. Recent years have seen occasional adult steelhead observations in the estuary and lower creek, suggesting the watershed retains some capacity for anadromous fish recovery. The upper watershed harbors resident rainbow trout populations in isolated pools, though connectivity remains compromised by barriers and seasonal dewatering.

Riparian vegetation along the creek includes willows, sycamores, and cottonwoods, though invasive species like giant reed (Arundo donax) have colonized extensive reaches. The creek corridor provides habitat for various bird species, small mammals, and amphibians, including the federally endangered arroyo toad in suitable upstream habitats.

Access to San Juan Creek is limited by private property in many areas. Doheny State Beach provides public access to the estuary, while portions of the upper watershed can be reached via trails in the Cleveland National Forest. The historic Mission San Juan Capistrano, founded in 1776, sits near the creek and represents a significant cultural landmark tied to the watershed's Spanish colonial history.

Recreational use remains constrained by low flows, water quality concerns during storms, and limited suitable paddling conditions. The creek functions primarily as an ecological corridor rather than a paddling destination, with restoration efforts focused on improving habitat connectivity and water quality for native species recovery.