Tomales Bay and its watershed are a resource-rich part of Marin County. Tomales Bay is included in the Gulf of the Faralones National Marine Sanctuary. It is also part of the Central California Coastal Biosphere Reserve and the Western Hemisphere Shorebird Reserve Network. The Audubon Society recognizes it as an important bird area.
In 2002, the U.S. Fish and Wildlife Service (USFWS) designated Tomales Bay as a Wetland of International Importance. The National Audubon Society has recognized the Bay as an “Important Bird Area.”
The Tomales Bay watershed has:
- Intertidal, subtidal, and benthic habitats
- Mud flats
- Salt marshes
- Freshwater marshes
Large eelgrass beds grow in the northern half of the Bay with smaller ones lining the eastern shore. Small islands provide roosts for birds and haul out areas for marine mammals.
The Tomales Bay area includes five main watersheds with a rich diversity of habitat types:
- Tomales Bay westshore
- Inverness subwatershed
- Lagunitas Creek
- Tomales Bay eastshore
- Walker Creek
Tomales Bay westshore
Tomales Bay's westshore contains some of the most ecologically significant coastal areas in California, including includes portions of Point Reyes National Seashore and Tomales Bay State Park.
The Inverness subwatershed is a collection of many small creeks draining into the west shore of Tomales Bay. These creeks include Haggerty Gulch, Fish Hatchery Creek, Redwood Creek, and First, Second, and Third Valley Creeks.
With limited residential and commercial development, the Inverness subwatershed along the westshore contains a diverse mix of native upland and aquatic habitats.
The Lagunitas Creek subwatershed is the largest drainage into Tomales Bay. Its major tributaries include:
- San Geronimo Creek
- Devils Gulch
- Cheda Creek
- Nicasio Creek
- Olema Creek
At the southwestern edge of the watershed, Olema Creek flows in nearly a straight line through a rift valley along the San Andreas Fault zone. The subwatershed includes the Kent, Alpine, Bon Tempe, Lagunitas, and Nicasio reservoirs.
The San Geronimo Valley is the last un-dammed headwaters of Lagunitas Creek, and is considered critical Coho salmon spawning and juvenile rearing habitat.
Lagunitas Creek originates on the steep, forested slopes of Mount Tamalpais. Its major tributaries include San Geronimo Creek and Olema Creek which meet to flow through Samuel P. Taylor State Park. Dense redwood growth along these creeks keeps water cool water year-round. These shady creeks provide spawning and rearing habitat for salmonids. Most of Lagunitas Creek downstream of the state park is thickly forested with willows and alders. Below Tocaloma Bridge, the Lagunitas watershed opens into a valley with broad, gently sloping hills. This area is primarily used for livestock grazing.
Tomales Bay eastshore
The small tributaries draining the east side of Tomales Bay include Millerton Gulch, Grand Canyon, Tomasini Canyon, and other unnamed tributaries. These small watersheds occur on both public and private lands.
Tomales Bay's eastshore is mostly grassland with oak-bay woodlands, coastal scrub, and eucalyptus. Fresh and saltwater marshes line Tomales Bay's eastshore. Scattered stands of coastal terrace prairie exist along the east shore's tributaries.
Topography in the 76-square mile Walker Creek watershed ranges from 1,500 feet to sea level where the creek empties into Tomales Bay just south of its mouth. The northern tributaries, Keyes Creek and Chileno Creek, flow through wide valleys with gentle, grassy hills. The upper watershed is much more rugged with extensive areas of coast live oak forest. The watershed contains a 220-acre natural lake, Laguna Lake, at the top of Chileno Valley. Soulajule Reservoir, constructed in 1968 in Arroyo Sausal and enlarged in 1980, is managed by the Marin Municipal Water District (MMWD).
Draining down into Tomales Bay's eastshore is the Walker Creek watershed. Walker Creek contains a mosaic of different habitats:
- Annual grassland
- Perennial grassland (near the coast)
- Valley foothill riparian forest
- Limited redwood forest
- Coastal scrub
- Oak bay woodlands
Laguna Lake in Chileno Valley is a shallow natural lake. Classified as a vernal pool, Laguna Lake retains water year round, though significantly less water in summer. The lake is used extensively by migrating and breeding waterfowl and amphibians. Wetlands at the mouth of Walker Creek provide important habitat for waterfowl.
Tomales Bay and its watersheds support over 900 species of plants and animals. Many are state and federally listed threatened or endangered species.
Special-status species found immediately in and around the Bay are:
- Saltmarsh common yellowthroat
- Great blue heron
- Great egret
- California black rail
- Coho salmon
- Chinook salmon
- Steelhead trout
- California brown pelican
- Steller sea lion
- California least tern
Approximately 45% of all bird species in North America have been recorded in the adjacent Point Reyes peninsula. Over 20,000 wintering shorebirds and up to 25,000 waterbirds use the shores both year-round and during migration. As many as 50,000 waterbirds depend on Tomales Bay during winter.
Approximately 300-600 harbor seals live in Tomales Bay. Gray whales forage at the mouth of the bay and at times enter the Bay. Pacific herring runs support a small commercial fishery. Tomales Bay has the second largest mariculture industry in the state.
Each of Tomales Bay's watersheds supports unique species populations.
Inverness subwatershed's baylands are used by seals and sea lions for foraging and as haul-out sites. California red-legged frog and northwestern pond turtle have been observed within the watershed. Dozens of mammals live in the Inverness subwatershed, including:
- Point Reyes jumping mouse
- Point Reyes Mountain beaver
- Southwestern river otter
- Several listed bat species
A significant population of wild Coho salmon still exist in the Lagunitas watershed and Pacific lamprey spawn in Lagunitas Creek. Until the early 1980s, green sturgeon used the lower reaches. Mountain lions are frequently seen in the watershed and river otters have been sighted in the mainstem of Lagunitas. An osprey colony has been active at Kent Lake since the 1960s and bald eagles have been sighted in recent years.
Other listed species currently observed in the watershed include:
- Northern spotted owl
- Steelhead trout
- California freshwater shrimp
- Foothill yellow-legged frogs
- California-red legged frog
- Chinook salmon
The grasslands of Walker Creek grasslands are an excellent places to find raptors including:
- Swainson’s hawks
- Ferruginous hawks
- Golden eagles
Restored riparian corridors in Chileno Valley attract a variety of neotropical songbirds species including:
The Inverness subwatershed is part of the West Marin Planning Area according to the 2007 Marin Countywide Plan. The desired outcomes for this planning area are:
- Maintaining the boundaries and character of existing villages
- Encouraging preservation of historic structures
- Keeping tourist facilities at a small scale
- Avoiding large-scale development
Over half of the Lagunitas Creek watershed is in public ownership. The upper part is owned and managed by Marin Municipal Water District for water supply. Samuel P. Taylor State Park is completely within the watershed boundaries. Point Reyes National Seashore and Golden Gate National Recreation Area manage extensive holdings north and west of Samuel P. Taylor State Park and in the Olema Creek and Bear Creek subwatersheds.
Lagunitas Creek watershed also has many small rural communities:
- San Geronimo
- Forest Knolls
- Lagunitas in San Geronimo Valley
- Point Reyes Station
Tomales Bay eastshore
Eastshore Tomales Bay is mostly private lands.
The Walker Creek subwatershed is almost all agricultural land use, with the exception of the town of Tomales. Beef is the primary agricultural product. There are a few dairies are left in the watershed.
Changes to the watershed
Granite-derived soils on the Tomales Bay westshore are very permeable and erosive. When these soils get saturated, this can cause landslides and debris flows that scour out creek channels. These sediment flows get deposited downstream in less steep channels, which often don't have enough tidal influence to move the sediments out to the Bay.
Over time, development has destabilized some of the west shore’s hill slopes. This has led to slumps and landslides during large rainfall events. Storms in 1982 and 1983 caused many road failures and landslides. Cumulatively, the sediment delivered by landslides, shift from grasslands to agriculture, and other land use change has altered the lower watershed.
In the mid-1800s, potatoes were loaded onto shallow barges in Keyes Creek downstream of the present day Highway One bridge. Looking at how narrow this same channel today, you can see how much the watershed has changed in 150 years. What once was navigable by a large barge is now better explored by a small canoe.
Tomales Bay's eastshore also has some mining in its history. Mercury was mined at three sites in the Walker Creek watershed after World War II. The largest mine, located at the Gambonini Ranch, closed in 1970.
Tomales Bay State Park offers public access facilities at Tomasini and Millerton Points and at a small parcel by Cypress Grove. On the eastshore, a public boat launch is available at Miller County Park by Nick's Cove.
The California Department of Parks and Recreation operates the Marconi Conference Center. Audubon Canyon Ranch owns and operates the 139-acre Cypress Grove educational reserve. Point Reyes National Seashore owns the former site of the historic town of Hamlet.
Restoration and conservation
Since the 1960s, the Walker Creek subwatershed has been the focus of several efforts to improve watershed health. Restoration seeks to address historic erosion and sedimentation problems, revive salmonid populations, and improve water quality for downstream fisheries.
In January 1982, a large storm destabilized the former Gambonini mine site and sent massive amounts of mercury-laden sediment into Walker Creek. The federal EPA and San Francisco Bay Regional Water Quality Control Board completed remediation of the site in 2000.
In 2005, the Regional Water Quality Control Board established a Total Maximum Daily Load (TMDL) for pathogens, to protect water quality in Tomales Bay for recreational uses and shellfish harvesting. TMDLs for nutrients, mercury, sediment and siltation are in progress.
Several agencies and non-profits help the ranching community meet these requirements. For example, the Marin Resource Conservation District developed the Conserving Our Watersheds (COW) Program. The program provides ranchers funding and technical support to implement voluntary resource conservation practices that meet TMDL objectives.
The National Park Service, in partnership with Audubon Canyon Ranch, has begun a program to restore more than 600 acres of wetland within the Waldo Giacomini Ranch and Olema Marsh, and to incorporate opportunities for the public to experience the restored wetlands.
- Point Reyes National Seashore website
- The Marin Coastal Watershed Enhancement Project.
- Survey of Eight Streams of the Inverness Ridge, Marin County, California.
- The Marin Coastal Watershed Enhancement Project.
- Distribution, Abundance and Implications for Conservation of Winter Waterbirds on Tomales Bay, California.
- Giacomini Marsh Restoration Site Special-status Animal Species: Reconnaissance and Compliance. Draft report to the National Park Service.
- The Kent Lake Osprey Colony, 40 years of growth and stability, Mt. Tamalpais symposium presentation.