The land draining into Stemple Creek is largely grassland with rolling hills for agriculture. Willows have been re-established along parts of the main creek and tributary streams. Coastal oak woodland can still be found along some of the higher tributaries. Eucalyptus, once planted in rows for windbreaks and fuel, are now one of the most common trees in the watershed.
Stemple Creek was a marginal Coho salmon and steelhead trout stream, until the early 1960s when a small dam built on the Button Ranch closed off the last available spawning areas.
Resident accounts tell of dense flocks of waterfowl. However, as in most areas along the Pacific Flyway, waterfowl numbers have dropped. Farm ponds, especially those with shallow edges, now provide some of the best remaining habitat for waterfowl, northwestern pond turtles, and other aquatic species.
California Department of Fish and Wildlife has identified the Estero de San Antonio and Estero Americano as among the most significant habitat areas in the State. They contain a remarkable mosaic of intermingling habitat types:
- Densely wooded riparian ravines
- Saltgrass areas, mudflats
- Eelgrass beds
- Small freshwater ponds.
The area between the two Esteros contains extensive areas of native coastal terrace prairie.
Special-status species in the watershed include:
- California freshwater shrimp
- Northwestern pond turtle
- Tidewater goby
- Myrtle’s silverspot butterfly
- California red-legged frog
The Estero is used by over 40 species of waterfowl and is an important winter feeding area for migrating birds. Golden eagles are known to nest in the upper watershed.
River otters have been observed in the Marin County portion of Stemple Creek east of Highway 1. Eelgrass beds in the Estero de San Antonio provide nursery habitat for Dungeness crabs.
Land use in the watershed is almost exclusively agricultural. 90% of the watershed is used for livestock grazing. The Marin County portion of the watershed contains mostly beef and sheep ranches, as well as some dairies. Sonoma County Agricultural Preservation and Open Space District and Marin Agricultural Land Trust are both active in the watershed, protecting agricultural land use through conservation easements.
Although the Estero de San Antonio is part of the Gulf of the Farallones National Marine Sanctuary, the land surrounding it is all privately owned. A sandbar often closes the mouth of the Estero in the summer or early fall. The Estero remains closed until winter rains with heavy runoff break open the sandbar. Since access across private land is by permission only, recreational uses are limited.
There are no cities or towns in the Stemple Creek watershed.
Changes to the watershed
An analysis of the Estero de San Antonio prepared for the 1994 Enhancement Plan found that 80% of the lagoon’s volume has been lost through historic sedimentation. This reduction in the area draining with the tides, or tidal prism, has led to an increase in the frequency and duration of lagoon closures from the sandbar that forms at the mouth. Evidence from the 1992/93 winter rains indicated that natural scouring of the lagoon bed could occur over time if sediment delivery to the Estero is reduced.
Conservation and restoration
In 1990, Stemple Creek was listed on the federal Environmental Protection Agency’s 303(d) list as an impaired waterbody due to excessive nutrients and sediment. Resource conservation efforts in the watershed to address these issues are extensive.
Enhancement Plan for the Stemple Creek/Estero de San Antonio watershed
In 1994, the Marin Resource Conservation District and Southern Sonoma County Resource Conservation Districts (now known as Sonoma RCD) completed an Enhancement Plan for the Stemple Creek/Estero de San Antonio watershed.
Implementation of that enhancement plan has been a decentralized effort. Although the two RCDs have led the way with grant-sponsored projects, local landowners have also implemented many measures on their own and with support from NRCS.
The Shrimp Club, a nationally-recognized project of Brookside School in San Anselmo, began its stream restoration work in Stemple Creek. The Shrimp Club and its successor, STRAW (Students and Teachers Restoring a Watershed, a project of Point Blue Conservation Science) have replanted native riparian vegetation for erosion control and habitat enhancement along many miles of Stemple Creek and its tributaries. Their efforts in the watershed are ongoing.
Total Maximum Daily Load and Attainment Strategy
In 1997, the North Coast Regional Water Quality Control Board adopted a Total Maximum Daily Load (TMDL) and Attainment Strategy for nutrients and sediment in the watershed. The TMDL has been adopted into the Basin Plan for the North Coast.
The Marin RCD has received Prop 50 funding for a project called “Conserving Our Watersheds: TMDL Implementation in Tomales Bay and Stemple Creek Watershed.” Through this program, the RCD supports ranchers in adopting voluntary conservation practices.
The 1994 Enhancement Plan states that over 80% of the accelerated erosion in the watershed comes from the lower watershed with large gully systems as the primary source. Gully stabilization projects have been implemented by local landowners with support from the RCDs and NRCS.
Watershed Protection and Flood Protection Act
The two RCDs and NRCS have collaborated to bring funding through the Watershed Protection and Flood Protection Act into the watershed to improve water quality.
Conservation Effectiveness Assessment Program
The Stemple Creek watershed has been designated one of 24 special emphasis watersheds as part of the NRCS’ Conservation Effectiveness Assessment Program (CEAP). This Program is a joint effort of the NRCS, UC Cooperative Extension, the Agricultural Research Service, and the Departments of Land, Air, and Water Resources and Plant Sciences at UC Davis. The purpose of the program is to test models for predicting the water quality impacts of conservation practices, and to evaluate the effectiveness of:
- Dairy waste management systems
- Riparian restoration
- Soil and water conservation practices