Aliso Creek is a 19.8-mile (31.9 km)-long, mostly urban stream in south Orange County, California. Originating in the Cleveland National Forest in the Santa Ana Mountains, it flows generally southwest and empties into the Pacific Ocean at Laguna Beach. The creek's watershed drains 34.9 square miles (90 km2), and it is joined by seven main tributaries. As of 2018, the watershed had a population of 144,000 divided among seven incorporated cities.