Through the heart of San Diego County runs the often-underappreciated aquatic gem that is the San Diego River. While most residents and visitors of the City are aware of the San Diego River (particularly when it is seen as a nuisance during times of heavy rain leading to excessive flooding as in this past winter), many may not realize that it provides an important ecological function to over 25 threatened, endangered and uncommon plant and wildlife species who call San Diego home for all or part of the year. The 52-mile river covers a variety of landscapes and habitat types, from its headwaters in the Cuyamaca Mountains to its mouth at the Pacific Ocean.
One of six major rivers in San Diego County, the San Diego River is highly visible to most people who live or visit San Diego as it traverses the densely populated Mission Valley. But the headwaters look quite different than what one observes while in the City limits. Rugged, remote, and wild, the upper San Diego River features boulder-filled steep and narrow canyons, with 1,000-foot drops creating cascading, seasonally dependent waterfalls. From the headwaters to the El Capitan Reservoir, you can expect to encounter Engelmann oak woodlands and may catch a glimpse of a golden eagle soaring overhead. When the sun begins to set, listen for arroyo toads singing during their breeding season of late winter to early summer. Mule deer, while wary, are highly dependent on the river as their main source of water and may be observed occasionally. And where there are deer, mountain lions will follow, and rely more than ever on these natural areas to escape the ever-increasing demands placed on their home range due to encroaching development.
From the El Capitan Reservoir, the river runs west through Mission Trails Regional Park, the seventh-largest open space urban park in the United States. A jewel in itself, Mission Trails Regional Park contains the five highest mountain peaks in the San Diego City limits and is one of the most biodiverse areas in the county. As the willow- and sycamore-lined San Diego River runs through Mission Trails Regional Park, it provides habitat for least Bell’s vireo, southwestern willow flycatcher, and yellow-breasted chat. Willowy monardella and San Diego ambrosia may be found along the edge of the river’s habitat, while coastal California gnatcatchers and coastal cactus wrens are often heard ‘mewing’ and ‘chattering’ in the coastal sage scrub in the adjacent uplands. Red diamond rattlesnakes, while more commonly occurring in the rocky outcrops in the hillsides above the river, will visit the riverbed for much needed water especially during years of extreme drought.
The San Diego River continues its flow west from Mission Trails Regional Park into Mission Valley and broadens into an estuary as it approaches the mouth at the Pacific Ocean. Along this broad stretch of river, pedestrians and cyclists are afforded a well-maintained walkway/bike path to enjoy the placid waters and expansive mudflats, where thousands of shorebirds, waterfowl, and gulls forage and roost during low tide. California least terns hover over the river before diving in to catch their prey, and western snowy plovers probe for aquatic invertebrates along the shoreline at the river’s mouth. As the river meets the ocean, estuary seablite and salt marsh bird’s beak occur in the coastal saltmarsh, while bat rays and round stingrays swim just under the surface of the water.
As biologists we often have the unique opportunity to survey and study often overlooked areas of our own hometown, whether it’s because these areas are remote and challenging to explore, or part of our everyday routine scenery. But I would encourage every San Diegan to become (more) acquainted with our riparian areas and rivers so that our residents can truly appreciate and value some of our local precious resources.
Brynne Mulrooney