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Protecting public health through water quality monitoring

Indicator bacteria are monitored in water samples from beaches, lagoons, streams, and groundwater to determine potential  health risks associated with exposure to fecal pollution. Sources of bacteria include improperly managed waste, stormwater runoff, animals, birds, septic tank discharges, livestock, and other activities that could mobilize pollutants. Bacteria levels are frequently elevated in the aftermath of rainfall and storm events.  

Coliform bacteria and Enterococci are indicator bacteria that are associated with fecal pollution. For beaches in Santa Cruz County, the levels of bacteria are compared to Standards for primary contact recreation to determine whether a Health Advisory should be issued and whether follow-up investigations are needed.

Water Quality Monitoring

Frequently Asked Questions about bacterial water quality

  1. What do the test results mean?
    The test results are reported as the 'Most Probable Number' of bacteria that are present in about  3 ounces of water (about the size of a small cup), referred to as MPN/100 mL. The MPN is a statistically-based estimate of the number of live microorganisms in the water sample.  The County uses standardized culture-based methods to determine the MPN/100 mL for each sample. The results are compared to standards set by the County, State, and USEPA.
    1. What does the water quality status mean?
      1. Water quality is considered ACCEPTABLE, when the bacterial levels are below the standards set by the County, the State of California, and the US Environmental Protection Agency.  
      2. Health Advisory is issued when the bacteria levels exceed any standards. The County conducts follow-up investigations at sites with recurring health advisories.
    2. What should I do if I swim at a beach that is under a Health Advisory?
      The County issues Health Advisories based on the most recent test results. In general, it is important to avoid swallowing water and to make sure you wash your hands carefully before touching any food. 
  2. How long does it take to get results from water quality sampling?
    The results from bacterial testing are generally available within 30 hours. 
  3. What causes changes in bacterial water quality?
    Rainfall and runoff can temporarily impact water quality and the County advises beachgoers to avoid water contact within 72 hours after rainfall. Tides, wind, offshore and onshore activities can also affect water quality. 

The County's water quality program focuses on:

  • Microbiological health risks : The County monitors indicator bacteria in ocean, freshwater, and groundwater. Molecular and biochemical tools are used to identify specific microorganisms and determine potential contamination sources.
  • Nutrients: Nitrogen and phosphorus are nutrients that can promote the growth of algae and disturb local ecosystems. Routine monitoring of  nutrients and other dissolved minerals in freshwater sources provides insights into seasonal or intermittent water quality perturbation. Drinking water systems can also be vulnerable to nitrate or nitrite contamination.
  • Cyanotoxins:  Microcystins, Anatoxin-a/Cylindrospermopsin are some of the toxins that are released by cyanobacteria in freshwater systems. The County monitors for toxins when there is evidence of an algal bloom, typically in the summer and fall months when the water temperatures increase and nutrient levels are elevated.