Pathogens and Nutrients

Pathogens, such as fecal coliform and Escherichia coli (E. coli), and nutrients, such as nitrogen and phosphorus are common pollutants in waterways across the US.

Pathogens have potential to present a health risk to wildlife and humans. Nutrients have potential to stimulate plant and algae growth in waterways, which in turn, leads to less oxygen in the water for aquatic life.

The San Francisco Bay Regional Water Quality Control Board (Regional Water Board) has studied pathogen and nutrient levels in the Napa River.

Currently, the Regional Water Board considers the recreation value of the Napa River to be impaired by pathogens and a Total Maximum Daily Load was enacted in 2007. The Regional Water Board considered the whole Napa River to be impaired by nutrients until 2014. However, in 2014, the Regional Water Board reviewed recently collected data and voted to have the upper portion of the Napa River removed from the US EPA's impaired list

The Napa River and its tributaries are listed as impaired by pathogens. The listing was made in response to observations of elevated bacteria in the river, which indicate the presence of fecal coliform contamination and health risks to recreational users of the river from water-borne pathogens.

Potential pathogen sources in the watershed include municipal stormwater, septic systems, sewer line leakage, pet waste, and livestock. The Napa River Pathogen TMDL examines this water quality problem, identifies sources of pathogen contamination, and specifies actions to create solutions. 

Multiple actions have been taken to reduce pathogens in the River:

  • adopting the statewide Onsite Wastewater Treatment Systems (OWTS) Policy to reduce pathogens from septic systems;
  • adopting statewide Waste Discharge Requirements (WDRs) for Sanitary Sewer Systems in 2006;
  • incorporating TMDL loads into the small municipal stormwater NPDES permit to regulate urban runoff;
  • adopting the Confined Animal Facility (CAF) WDRs in 2016;
  • adopting the Grazing Operations WDRs in the Napa and Sonoma Watersheds in 2011.

Future implementation actions include reissuance of Grazing WDRs, approval of the Napa County OWTS management plan, regulation of horse boarding facilities and other CAFs, and continued monitoring.

Review the Regional Water Board's Report Card for Napa River Pathogens on the Water Board's website. 

The Napa River and its tributaries provide habitat for a diverse array of aquatic life, including steelhead trout and Chinook salmon. However, by the 1970s, nutrient loading from onsite wastewater treatment systems and agricultural lands contributed to high nutrient levels in the Napa River. As a result, the Napa River was added to the state’s Clean Water Act (CWA) section 303(d) list of impaired waters in 1976 for nutrients (excess nitrogen and phosphorous).

Landowners, local watershed organizations, and many federal, state and local government agencies collaborated to implement nonpoint and point source control measures to reduce nutrient loading to the river. Due to these efforts, nutrient levels have decreased. As such, in 2014, the Regional Water Board recommended that the non-tidal portion (36 miles) of the river be removed from the CWA section 303(d) list for nutrient impairment. All reports and data for this recommendation can be found at this link.

This delisting recommendation will be included in the Integrated Report submitted to U.S. EPA for the 2018 listing cycle. The Regional Water Board estimate's the State Board hearing on the 2018 list will occur in summer 2020.