The North Coast Regional Water Quality Control Board (Regional Water Board) is responsible for developing and enforcing water quality objectives and implementation plans that will best protect the beneficial uses of the State’s waters. Over the past 25 years, the Regional Water Board has monitored surface waters for the presence of pathogenic bacteria potentially indicative of water contamination. Sources of these bacteria include the natural environment (soils and decaying vegetation), stormwater, urban runoff, animal wastes (both wildlife and domestic animals), and human sewage. Analysis for total and fecal coliform, Enteroccoccus sp., and Escherichia coli bacteria are widely used as indicator tests. Coliform is a heading that describes a type of bacteria, which includes E. coli. It is found within the intestines of warm blooded animals, though most water contamination comes from cattle and people. Enterococcus sp. is similar to coliform bacteria, but is known to have a greater correlation with swimming-associated illnesses and is less likely to die-off in highly saline water. While these bacteria normally occur at low levels in the environment, high levels can indicate contamination and the presence of other harmful pathogens. These pathogens, if contacted, could result in such symptoms as diarrhea, cramps, and nausea. Bacteria water quality objectives are described in the Water Quality Control Plan, North Coast Basin (Basin Plan) and are based off of guidelines established by the California Department of Health Services (CDHS) in the Draft Guidance for Fresh Water Beaches.

The CDHS has the following draft guidelines:

  • Total Coliform: 10,000 MPN per 100 ml
  • Fecal Coliform: 400 MPN per 100 ml
  • Enterococcus: 61 MPN per 100 ml
  • E. coli: 235 MPN per 100 ml

These guidelines have not been adopted as a standard at this time, which means that they may change and that they are not enforceable. The Basin Plan objectives for fecal coliform state that median 30-day levels (based on a minimum of 5 samples/30 days) should not exceed 50 MPN per 100 ml and that no more than 10% of those samples should exceed 400 MPN per 100 ml. A 30-day median is determined by arranging the daily sampling values in ascending order (ex 20, 30, 50, 80, 120) and selecting either the middle number in that arrangement (50) or, if there is no one median number (20, 30, 50, 80) the mean of the two centermost (40). Levels that do not meet Basin Plan objectives do not necessarily pose a health threat, but instead indicate the need for further investigative sampling.


Regional Water Board Monitoring Program
Regional Water Board North Coast Basin Plan
California Department of Health Services Guidance for Freshwater Beaches