The San Diego River begins as a trickle in the Cuyamaca Mountains northwest of the town of Julian. It then flows to the southwest until it reaches the El Capitan Reservoir and continues west through Santee and then Mission Trails Park on its way to the Pacific Ocean. Where the river and ocean meet, it formed the estuary that became the world’s largest manmade water park: Mission Bay. There is still an estuary there, a small one mostly contained by a concrete embankment and sandwiched between the south Mission Bay Jetty and Dog Beach.
In the 1820s, due to flooding and the resulting buildup of silts, the river began dumping into San Diego Bay. In 1877, to prevent the buildup of silts in the busy harbor, a levee was built to divert the river back to where it now flows.
In 2001, the San Diego River Park Foundation was established to promote the creation of a 52-mile-long system of parks, trails, and open spaces along the San Diego River. Clean-up projects and water-quality testing are among the ongoing efforts to return the river and its banks to a more natural state.