Frequently Asked Questions

How do I know that it is safe to swim at my local beach?
Over the past 40 years, the Health Care Agency and two local sanitation agencies (the Orange County Sanitation District and South Orange County Wastewater Authority) have been testing the coastal ocean, bay and harbor waters in Orange County for bacteria that indicate the possible presence of disease causing organisms. The results of the tests are reviewed by Health Care Agency Environmental Health staff, and if the data indicates a contamination, warning or closure signs are posted at the beach depending on the extent and cause of the contamination. Signs are posted at locations where contamination was detected so that you will know where it is not recommended to swim. You may also call the Beach Closure and Posting Hotline at (714) 433-6400 or click on the “Beach Closures & Warnings” icon on the menu to find the latest status of a beach.

The Health Care Agency and the sanitation agencies routinely collect water samples at approximately 150 ocean, bay, harbor, storm drain, creek and river locations along the shoreline of Orange County. Water samples are collected in sterile bottles according to specific guidelines. Sampling staff typically collect samples in ankle deep water using a long pole with a sample bottle attached to the end to scoop up the water. Sample bottles are immediately capped and placed into an ice chest with “blue ice” for preservation. The time, date, weather conditions and location of collection are recorded on a log sheet. Samples are then transported to the laboratory for analyses.

The frequency of sample collection ranges from at least weekly to five times per week along the Orange County coastline, depending upon the requirements of the agency collecting the samples. When the results of testing indicate a contamination problem exists, the sampling frequency and locations around the original sample location may increase until the sample results are within standards and/or the source of the problem is determined.

Water samples are analyzed for indicator bacteria – total coliform, fecal coliform and enterococcus – which indicate possible pollution from numerous sources including fecal waste. They are called indicator bacteria because they are relatively easy to collect and analyze, and may show the presence of harmful viruses, bacteria or protozoa (also known as pathogens). Collecting and measuring the disease-causing organisms directly is difficult. Sources of indicator bacteria may be:

  • Environmental – soils, decaying vegetation
  • Animal wastes – birds, dogs, cats or rabbits
  • Humans – sewage, kids with diapers, shedding from body
  • Storm water or urban runoff

There are three ways that water samples are analyzed for indicator bacteria. The results of each of these techniques are considered to be equivalent.

Membrane Filtration Technique – Uses extremely fine paper filters through which the water sample is passed. These filters are then placed on bacteriological growth media that contain food specific to the indicator bacteria (total coliforms, fecal coliforms and enterococci). If these bacteria are present, they will grow on the filter and form colonies. These colonies are counted and the number of the original bacteria present in the water sample calculated. Results for the membrane filtration technique are reported as the number of colony forming units (CFU) per 100 milliliters of water sample or CFU/100ml. All three of the agencies collecting and analyzing ocean and bay samples in Orange County (the Health Care Agency and two local sanitation agencies – Orange County Sanitation District and South Orange County Wastewater Authority) use the membrane filtration method.

Multiple Tube Fermentation Technique – Uses test tubes containing nutrient broth or food (media) specific to the indicator bacteria. These tubes are inoculated with several dilutions of the original water sample. The presence of indicator bacteria is evidenced by the production of carbon dioxide gas, an end product of lactose fermentation. After the positive tubes are tallied, a statistical technique is used to determine the concentration of bacteria in the sample. Results for this technique are reported as Most Probable Number (MPN) of bacteria per 100 milliliters of water sample or MPN/100 ml.

Defined Substrate Technology Technique – Uses a multiple well tray test kit to detect the presence or absence of indicator bacteria. The detection of indicator bacteria is based on a color change of the media in the wells to yellow or yellow with fluorescence. Results for this technique are reported as Most Probable Number (MPN) of bacteria per 100 milliliters of water sample or MPN/100 ml.

The results of shoreline bacteriological testing are reviewed on a daily basis. The status of ocean and bay waters can include:

Open: Test results indicate that levels of bacteria are below state standards.
Closed: Areas that have been impacted by an unauthorized discharge of sewage are closed to water-contact recreation and are posted with closure signs. Beach goers can visit and enjoy the beach, but should avoid contact with ocean or bay waters in the closed area.
Warning: Test results indicate elevated levels of bacteria exceeding standards in the ocean or bay waters at this location. Beach goers should avoid contact with waters in the area posted with warnings. Usually 150 feet upcoast and 150 feet downcoast of the sampling location is posted. Storm drain, creek or river water as well as the ocean or bay water impacted by runoff should also be avoided.
Advisory: Storm water runoff can make Orange County coastal waters unsuitable for swimming for at least 72 hours (three days) after a rainstorm. Coastal beaches and bays impacted by storm water runoff from storm drains, rivers and streams, and the runoff itself should be avoided by beach goers.

The California Ocean Water-Contact Sports Standards are found in the California Code of Regulations – Title 17 and the California Health and Safety Code.

Single Sample Standards:

Total coliforms

10,000 organisms/100 milliliters of sample

Fecal coliforms

400 organisms/100 milliliters of sample


104 organisms/100 milliliters of sample

Fecal:Total coliform ratio

>1000 total coliforms if ratio exceeds 0.1

30-day geometric log mean standards of 5 weekly samples:

Total coliforms

1000 organisms/100 milliliters of sample

Fecal coliforms

200 organisms/100 milliliters of sample


35 organisms/100 milliliters of sample

Polluted runoff and untreated sewage released into bathing waters may result in swimmer exposure to pathogenic bacteria, viruses and protozoans. These disease-causing organisms may be present at or near the site where the polluted discharge enters the water. The following table lists the types of organisms and the diseases (or symptoms) they may cause.

Pathogenic Agent



E. coli


Salmonella (not typhi)

Gastroenteritis, usually with fever; less commonly septicemia (generalized infection -organisms multiply in the bloodstream)

Some strains of Shigella

Gastroenteritis, usually with fever

Protozoa (Intestinal Parasites)


Diarrhea – Cryptosporidiosis

Giardia lamblia

Diarrhea – Giardiasis





Respiratory infection, rash, fever; meningitis

Norwalk and Norwalk-like viruses



Respiratory infection and gastroenteritis

Hepatitis A (outbreaks associated with eating shellfish from sewage-contaminated water)

Infectious hepatitis (liver malfunction)

The levels of bacteria, viruses and protozoa decrease over time due to the following reasons:

  • Die off due to sun (ultraviolet exposure), salt water or age;
  • Predation by other organisms; and
  • Dilution.

Everyone can help improve water quality at the beach no matter where they live, work or play. Runoff from anywhere in Orange County eventually ends up at the beach and with the runoff, all the bacteria, litter, oil or grease it picks up along the way. Many of the storm drains lead to the beach, not to a treatment plant. Some easy things we can do to help include:

  • Properly dispose of animal waste. Use a “doggie bag” when walking your dog and dispose in a trash can. Pick up after your cat.
  • Use a broom rather than a hose to clean driveways and sidewalks. Control irrigation flows to minimize runoff.
  • Properly dispose of household paints, chemicals and motor oil. Never pour chemicals on the ground or down storm drains.
  • Don’t feed wild animals or birds. Their droppings can significantly increase bacteria levels in the ocean or bays.
  • Don’t litter along highways and sidewalks. When visiting the beach, pick up all your trash and help out by picking up litter.
  • Wash your car on the lawn or take it to a car wash to avoid runoff.

Remember, the ocean is closer than you think – it begins at YOUR front door!

Tar balls are little, dark-colored pieces of oil that can sometimes stick to your feet when you go to the beach. They can be from natural occurring seeps, places where oil slowly escapes from the earth surface above petroleum reservoirs, or are remnants of oil spills. Tar balls have been found to form naturally from seeps located in Southern California, including in Orange County.

For most people, an occasional brief contact with a small amount of oil, while not recommended, will do no harm. However, some people are especially sensitive to chemicals, including the hydrocarbons found in crude oil and petroleum products. They may have an allergic reaction or develop rashes even from brief contact with oil. In general, we recommend that contact with oil be avoided. If contact occurs, wash the area with soap and water, baby oil, or a widely used, safe cleaning compound such as the cleaning paste sold at auto parts stores. Avoid using solvents, gasoline, kerosene, diesel fuel, or similar products on the skin. These products, when applied to skin, present a greater health hazard than the tarball itself.

If you notice unusual numbers of tar balls on the beaches, call the U.S. Coast Guard any time at 800.424.8802. Click here for more information on tar balls.