San Lorenzo Creek Watershed
The San Lorenzo Creek Watershed, at 48 square miles, is one of the largest watersheds draining to the eastern shore of San Francisco Bay. The watershed begins in the East Bay hills at the Dublin Grade, incorporates the unincorporated communities of San Lorenzo, Ashland, Cherryland, Fairview, and Castro Valley, and includes portions of San Leandro and Hayward. San Lorenzo Creek flows generally west, entering central San Francisco Bay near Roberts Landing, west of San Lorenzo.
The lower and middle watershed areas are highly urbanized and the natural drainage has been greatly altered. The lower portion of San Lorenzo Creek, for example, starts at Mission Boulevard and runs in a concrete channel 4.6 miles to the creek mouth. Similarly the formerly independent Sulphur Creek was diverted into San Lorenzo Creek in the 1960s to reduce the risk of flooding in downtown Hayward. The upper watershed, including the subwatersheds of Cull Creek, Crow Creek, and Palomares Creek, is less urbanized and includes most of the 105 miles of open creek that exist within the greater watershed. The watershed also includes two lakes that were created in the early 1960s with the construction of Cull Creek Dam and Don Castro Dam.
Flora and Fauna
Steelhead historically inhabited much of the San Lorenzo Creek Watershed until channelization and other effects of urbanization led to degraded trout habitat and decreased populations. Steelhead were relatively abundant into the 1950s, but construction of the Don Castro and Cull Creek dams in the early 1960s completely blocked anadromous fish migration into large portions of the upper watershed. Although suitable habitat for rainbow trout and steelhead still exists, passage barriers, excess fine sediment, periodic poor water quality, and other factors limit the numbers and distribution of these fish. Refer to the Friends of San Lorenzo Creek’s website for the current status of fish populations in the watershed.
Common native plant species that inhabit the oak woodland and grassland communities of the upper watershed include California poppy, coyote brush, California sage, and coast live oak. Many of the riparian corridors of the watershed include a wide variety of native plants both in the understory and canopy. Some species include California wild rose, California blackberry, willow, box elder, and big leaf maple. However, a plethora of non-native plants generally outcompete the native flora; these include cape ivy, periwinkle, and pampas grass. For more information on native plants and identification of plant species, contact the East Bay chapter of the California Native Plant Society.
Geology and Hydrology
Powerful geologic processes such as uplift, earthquakes, erosion, and mass wasting created the San Lorenzo Creek Watershed. In the East Bay hills, the watershed is underlain by rocks formed on or beneath the sea floor over 60 million years ago. Exiting the hills in downtown Hayward, San Lorenzo Creek crosses the Hayward Fault, a major earthquake fault that extends the length of the East Bay. From there to the bay, the creek flows across urbanized flatlands underlain by layers of sand, gravel, silt, and clay eroded from the hills and deposited by the creek and its tributaries. A U.S. Geological Survey (USGS) hydrology study completed in 2003 gives a detailed description of the natural processes that formed and continue to form the San Lorenzo Creek Watershed.
The middle and lower watersheds drain primarily urban areas, so surface runoff carrying potentially harmful pollutants is a significant concern that affects the health of the creeks and eventually San Francisco Bay. These pollutants include fertilizers, pesticides, animal waste, heavy metals, and gas and oil. The creeks also transport a significant amount of litter to the shoreline and the bay, particularly lightweight plastic products. Invasive plants, flooding, and erosion also pose threats to the open sections of creek. A major issue for both Cull Canyon and Don Castro reservoirs is siltation. Eroded silt from upstream creeks continually fills in the reservoirs, which reduces their capacity to hold stormwater. The siltation also jeopardizes water quality and impedes recreation.
Flora and Fauna
The northern section of the Upper Alameda Creek Watershed is home to a multitude of native plant and animal species. Characterized by a wide range of vegetation communities – grasslands, sage / scrub lands, oak woodlands, and riparian forest – the undeveloped areas of this section of the watershed contain a variety of native plants, including some special status species like the fragrant fritillary, maple-leaved checkerbloom and most-beautiful jewelflower. Small pockets of unique vegetation types such as alkali wetlands, fresh water marshes and alkali meadows are scattered throughout the area as well, concentrated in the Arroyo Las Positas Subwatershed.
These vegetation communities also provide habitat for many native birds, amphibians, reptiles, bats and other mammals. The waterways and waterbodies within the northern section of Upper Alameda Creek Watershed provide especially important habitat, as the edges of ponds and the riparian areas along creeks are home to special status species such as the California red-legged frog, California tiger salamander, western pond turtle, and tri-colored blackbirds. Historically, the creeks in the northern section of the Upper Alameda Creek Watershed hosted over a dozen native fish species. Although anadramous species are no longer able to access the upper reaches of the watershed due to downstream barriers, other native fish – like riffle sculpin, hardhead and rainbow trout – still utilize these creeks.
Geology and Hydrology
The northern section of the Upper Alameda Creek Watershed is comprised of steep hills and deep canyons in the rural areas which give way to the Livermore, Amador and San Ramon Valleys. This topography was largely created by the Calaveras fault, which runs from Danville to the area south of the Calaveras Reservoir. Many of these steep slopes are comprised of soil types that are prone to erosion, which can lead to increased runoff and sediment within streams in large storm events or if the land is not managed properly. (Learn more about the different soil types found in the watershed here.)
As with many other watersheds throughout the Bay Area, hydrology in the northern section of the Upper Alameda Creek Watershed shows high seasonal variation and periods of drought, with groundwater levels and stream flows high during the rainy winter months and significantly lower during hotter months in the summer and fall. Flows in many creeks are not even visible during these summer months, retreating below ground and resurfacing upon reaching larger streams. The well-draining soils in the valleys drain rain and creek water and recharge large groundwater basins that lie beneath the Livermore Valley. Additional recharge is planned to occur as the use of the gravel mining pits within the Chain of Lakes subwatershed is shifted to stormwater detention, and surface water storage and conveyance.
The largest issue in this portion of the Upper Alameda Creek Watershed is the rapid growth of the urban and suburban areas of Dublin, Pleasanton and Livermore. Developed areas often contain large amounts of impervious surfaces, which reduce groundwater recharge and may increase contaminants and litter in surface water (such as creeks). Creeks flowing through urban areas are often channelized to control flows and alter stream location. Channelization, which often includes straightening a creek’s natural path, can reduce the amount of native riparian habitat along creek banks and create an environment that is inhospitable for native plants and animals.
As with the rest of the Alameda Creek Watershed, dams create barriers for upstream fish migration to the northern section of the Upper Alameda Creek Watershed. This portion of the watershed is not currently accessible to steelhead, although this species was historically present and have been observed downstream from barriers.
Major Creeks & Waterbodies
San Lorenzo Creek
San Lorenzo Creek is fed by over 13 named tributary creeks and two constructed lakes. The majority of these tributaries lie in the upper watershed where they generally flow in natural open channels. As these creeks merge into San Lorenzo Creek, the impacts of urbanization increase until the creek finally reaches the bay through an engineered channel.
Middle San Lorenzo Creek Watershed
The middle watershed encompasses nearly 10 square miles and is more developed and less rural than the upper watershed. Four creeks define this watershed: Chabot Creek, Castro Valley Creek, San Lorenzo Creek from Don Castro Reservoir to Foothill Boulevard, and Sulphur Creek. These creeks are a highly fragmented combination of natural creeks, culverts, and concrete channels that run through the urban-rural interface. The exception is San Lorenzo Creek which is generally intact but confined by urban encroachment.
Lower San Lorenzo Creek Watershed
The lower watershed extends from Foothill Boulevard in Hayward to the San Francisco Bay and is highly urbanized. Development in the area includes single-family homes and apartment buildings, as well as a variety of commercial uses. San Lorenzo Creek flows in engineered channels through this entire reach with little or no riparian habitat present.
Cull Canyon and Don Castro Reservoirs
Cull Canyon and Don Castro reservoirs were built in the 1960s and are maintained by the Alameda County Flood Control and Water Conservation District for flood control purposes. These reservoirs have siltation issues and have been slowly filling since their creation, lessening their ability to hold stormwater. The two reservoirs are the centerpieces of their eponymous recreation areas, which are operated by the East Bay Regional Park District and are popular East Bay swimming spots.
Publicly accessible hiking, walking, and biking trails provide a wide range of recreational opportunities. A number of regional and city parks also offer access to many creeks and water bodies.
The 500-mile-long Bay Trail crosses through the Hayward Regional Shoreline and offers views of San Lorenzo Creek. The trail provides easily accessible recreational opportunities for outdoor enthusiasts such as hikers, joggers, bicyclists, and skaters, as well as opportunities for wildlife viewing and environmental education.
In 1992, over 100 miles of trail in the San Lorenzo Creek Watershed was added to the Bay Area Ridge Trail, taking hikers all the way from Don Castro Reservoir past Cull Canyon Reservoir and along Cull Creek, crossing Crow Creek on the way. In some areas the trail follows city streets or wide service roads; in others it may follow a creekside path under a shady canopy or meander through gently contoured grasslands to high meadows. In all, the Bay Area Ridge Trail traces 340 miles of ridgeline around San Francisco Bay.
Parks and Recreation
Bay Trees Park
This park provides a view of the junction of Crow Creek and Cull Creek, both in concrete channels. The far channel, Crow Creek, is floored with sand and debris deposited by the creek during high flows, whereas the Cull Creek channel is fairly clean, as its sediment is caught by the reservoir upstream. A walk upstream past the picnic area affords views of the dam spillway.
Cull Creek was dammed in 1963 to control flooding downstream, creating a 1.5-acre lake. The creek now deposits its sediment in the reservoir which must be periodically dredged to maintain flood storage capacity. The recreation area offers swimming and fishing in the lake and access to the Bay Area Ridge Trail.
Earl Warren Park
Located adjacent to Creekside Middle School on Center Street in Castro Valley, Earl Warren Park consists of an open lawn, play area, and dog park next to Crow Creek where it flows above ground on its way to Don Castro Reservoir.
Carlos Bee Park
This narrow park is tucked between Chabot Creek and an adjacent hillside. Walking paths offer views of the creek that, freed of its artificial confines, rushes over bedrock and cascades through a shady gulch. At the eastern end of the park, the trail descends to the water.
De Anza Park
Spanish explorers who camped here on the banks of San Lorenzo Creek in the late 1700s found a reliable water source lined with alders, cottonwoods, and willows. Visitors can climb down the steps beneath a canopy of mature trees to view the creek. This is the final undeveloped reach of the creek before it flows under Foothill Boulevard and into a concrete channel built in 1954 for flood control.
The lagoon and adjacent lake were created in 1964 when the Alameda County Flood Control and Water Conservation District dammed San Lorenzo Creek. The Don Castro Reservoir is now closed to boating and swimming but open to fishing and hiking along its shore. The Don Castro Regional Recreation Area comprises 101 acres in its entirety, offering swimming in the lagoon, fishing, and hiking trails including access to the Bay Area Ridge Trail.
This park includes salt marsh and mudflats where San Lorenzo Creek flows into the bay. Visitors can bike or walk the shoreline trail to the interpretive center or take the San Francisco Bay Trail to the mouth of San Lorenzo Creek.
Perched on stilts above a salt marsh, the Hayward Shoreline Interpretive Center offers an introduction to the ecology of the San Francisco Bay Estuary. It features exhibits, programs, and activities designed to inspire a sense of appreciation, respect, and stewardship for the bay, its inhabitants, and the services they provide.
The gardens, tucked between Castro Valley Creek and San Lorenzo Creek, are open to the public and are also available for weddings.
The Meeks built their estate along San Lorenzo Creek in 1868 and planted the grounds in orchards. It was here that Mr. Bing, Meek’s Chinese orchardist, developed his famous cherry. The concrete channel of San Lorenzo Creek behind the estate was built in 1962 as a federal flood control project.
The mission of the Sulphur Creek Nature Center is to instill a sense of responsibility for the welfare of our world by bringing people and animals closer together through wildlife rehabilitation and education. The nature center offers educational programs and viewing of some of the Bay Area’s native wildlife.
- Alameda County Clean Water Program
- Alameda County Resource Conservation District
- Bay Ridge Trail
- California Native Plant Society
- East Bay Regional Park District
- Hayward Area Recreation & Park District (H.A.R.D.)
- Friends of San Lorenzo Creek
- Oakland Museum of California’s Guide to Bay Area Creeks
- USDA Natural Resources Conservation Service