Tomales Bay Pathogen TMDL

Tomales Bay Pathogen TMDL adopted and approved
On February 8, 2007, the U.S. EPA approved the TMDL for pathogens in Tomales Bay. The Basin Plan has been amended to incorporate the TMDL along with an implementation plan to achieve the TMDL. The amendment was adopted by the Regional Water Board on September 21, 2005. The TMDL was approved by the State Office of Administrative Law and became effective on September 13, 2006.

TMDL Implementation

Grazing Waiver Program

STATUS UPDATE (12/23/13)
On December 11, 2013 the San Francisco Bay Water Board renewed the Conditional Waiver of Waste Discharge Requirements for Grazing Lands in the Tomales Bay Watershed (2013 Grazing Waiver) for a second, five-year term. The 2013 Waiver implements the Tomales Bay Pathogens TMDL (Total Maximum Daily Load), the Walker Creek Mercury TMDL, and the Tomales Bay Mercury TMDL.

For any questions regarding the Waiver or Waiver compliance, please contact Réne Leclerc 510.622.2410 or e-mail For further information about the Grazing Waiver program please visit the Grazing Waiver Program page.

Marshall Community Wastewater Treatment System

STATUS UPDATE (05/31/16)
On April 20, 2016, public health officials in Marin County celebrated the successful completion of the Marshall Community Wastewater Treatment System, a project that serves about 50 properties on the eastern shore of Tomales Bay. This marked completion of the second phase of this project; the total cost of the two phases was $3.2 million. Water Board staff played important roles in the design, upgrade and oversight of State Water Board assistance grants for this community wastewater system. 

The impetus for this work was the Tomales Bay Pathogens TMDL Implementation Plan, which called for actions to address onsite wastewater treatment systems (septic systems) as they were identified as one of the sources contributing to water quality impairment. 

Post TMDL adoption, Marin County initiated Phase 1 of the Marshall Community Wastewater Treatment Project by replacing or upgrading existing privately-owned septic systems and constructing a new community-scale and publicly owned wastewater collection, treatment, and land-discharge system. In 2007, the property owners in the northern part of Marshall voted to form a Special Assessment District to help pay for Phase 1 of the project which addressed 30 parcels. With additional funding from the State Water Board, the U.S. Environmental Protection Agency, and the County, construction began shortly thereafter. The project entailed the replacement or upgrade of septic tanks and the installation of pumping and control equipment on each property, construction of a new mile-long pressure sewer line, and installation of a common leachfield on a 6-acre site purchased by the County from a local landowner.

The second phase of the project began in June 2013, when the State Water Board awarded a $750,000 grant to the County, with matching funds from the County and property owners, to design and construct additional wastewater facility improvements for approximately 20 residences and businesses located along the southern shoreline of Marshall.

Bacterial Water Quality Monitoring Program

STATUS UPDATE (05/31/16)
In fall 2014, Water Board and Tomales Bay Watershed Council (TBWC) Staff agreed to combine resources and collaborate on a single water quality monitoring program for the Tomales Bay watershed. The new collaborative monitoring plan, which also utilizes the National Parks Service’s as well as the Inverness Public Utility District’s staff resources, collects samples at approximately 30 stations on a monthly basis. In addition, each year these stations are also monitored weekly for five weeks during both wet and dry seasons. For more information about the TBWC water quality monitoring program please visit their web page.  

NEW - Fall 2023 - Long-term Bacteria Water Quality Monitoring Map
The San Francisco Bay Regional Water Board has created a map to illustrate the results of the long-term bacteria water quality monitoring in the Tomales Bay watershed. The map visually demonstrates pre- and post-TMDL bacteria levels, as well as the rate at which they exceed the applicable water quality objective for water-contact recreation at various sites within the watershed.


Tomales Bay supports a vital shellfish industry and is a popular destination for recreation, such as swimming and boating. It also faces water quality challenges from pathogens, water-borne micro-organisms that can cause disease in humans. Pathogens in Tomales Bay are of fecal origin. Potential sources include agricultural runoff (from dairies and ranch lands), runoff from residential areas, failing septic systems or small wastewater treatment facilities, discharges from boats, and wildlife. The Tomales Bay Pathogen TMDL includes a broad-based strategy for reducing pathogen sources to the Bay, including increased regulation of grazing lands through waste discharge requirements, required actions to reduce polluted runoff and boat discharges, education and outreach, and monitoring to evaluate progress. Photo of a small boat on Tomales Bay

TMDL Map for Tomales Bay

The San Francisco Bay Regional Water Quality Control Board has created a map of long-term bacteria monitoring in and around Tomales Bay. Watershed Stewards Program Corpsmembers and Scientists from the SF Bay Regional Water Quality Control Board created this map to visually demonstrate Pre and Post TMDL bacteria levels in and around these water bodies. The purpose of the Web Maps is to represent bacteria loads from pre-TMDL sampling, post-TMDL - sampling, and the present.

For more information contact:
Farhad Ghodrati
Environmental Scientist
1515 Clay Street, Suite 1400
Oakland, CA 94612
Phone: 510-622-2331
Fax: 510-622-2460