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Recreational Water

Massachusetts has over 1,000 freshwater and marine beaches. The U.S. Environmental Protection Agency (USEPA) and Massachusetts Department of Public Health (MDPH) require that these beaches be monitored for bacteria. The presence of these bacteria can indicate when the water is polluted and people should not be swimming. Swimming in polluted water can lead to illnesses, such as nausea, sore throat, earache, skin rash, or fever.

Did You Know?

Approximately 15,000 water samples are collected each year at over 1,000 marine and freshwater beaches in Massachusetts.

Since 2001, MDPH's beach regulations (105 CMR 445.000: Minimum Standards for Bathing Beaches) have required that all public and semi-public beaches in the state be monitored for bacteria during the beach season. Examples of semi-public beaches include beaches at summer camps, hotels, condominiums, and country clubs.

Pollution in beach water is often associated with human or animal waste, which may enter the water in a variety of ways, including:

  • stormwater runoff
  • leaking sewer pipes
  • combined sewer overflows (a release of untreated sewage with rainwater)
  • illegal sewer hookups
  • poorly functioning septic systems
  • discharge of sewage by boats
  • pet waste

Most illness-causing organisms are difficult to measure directly, but water samples that contain them also contain bacteria which are easier to measure. When the presence of one organism is used to indicate the presence of another, it is referred to as an "indicator." These "indicator organisms" provide an indication of the presence and quantity of illness-causing organisms in the water.

In Massachusetts, the types of bacteria used as indicator organisms at marine beaches are enterococci and at freshwater beaches are either enterococci or Escherichia coli (E. coli). MDPH's beach water quality standards are displayed in the table below. The values given are in colony forming units per 100 milliliters of water (cfu/100 ml), which is a standard way of measuring bacteria in water.

Single sample maximum

Geometric mean

Marine

Enterococci

104

35

Freshwater

Enterococci

61

33

E. coli

235

126

The single sample maximum is the MDPH standard for the amount of bacteria in the water that should not be exceeded and reflects short-term conditions. It is used to protect swimmers from a brief exposure to high levels of bacteria. The geometric mean is calculated from the five most recent non-rain event samples and is used as an indicator of the water quality over an extended period of time. It was developed to protect swimmers from potential long-term exposures to levels of bacteria that are below the single sample maximum value, yet consistently elevated.

Water samples that contain levels of bacteria above regulatory standards are called exceedances. Depending upon the water quality history at the beach, either a single or two consecutive exceedances will trigger a beach posting. When this happens, signs must be posted at access points to the beach to notify the public that swimming is unsafe. For marine public beaches, the public is also notified via the Beach Water Quality Locator, accessible from the MDPH/BEH website. Beaches must remain posted until bacteria counts decrease to levels below the standard.

Data Considerations

When reviewing and interpreting water quality data, it is important to take into consideration the following:

  • Many factors can affect whether exposure can lead to a health problem, including level of contamination, type of exposure (ingestion, inhalation, dermal, orbital, aural, nasal), and the length of contact time with contaminated water. Some populations may be more susceptible to health problems following exposure, such as pregnant woman, children, and immune suppressed individuals.
  • The exact dates of a given beach season vary from beach to beach, and are determined by the beach’s operator. Some beaches open as early as Memorial Day, but the majority begin operation when the school year ends in mid-June, and most close for the season around Labor Day.
  • The minimum frequency of monitoring required by MDPH is weekly. Some beaches with water quality issues may be monitored more frequently. Beaches with very good water quality may be tested less frequently than weekly, usually one to two times a month.
  • Beginning in 2014, depending upon the water quality history at the beach, either a single or two consecutive sample results that exceed the regulatory standards may trigger a beach posting.
  • When using non-detect values in calculations, one half the detection limit is substituted (for example, if the reported result is <2, the value used in a calculation is 1).

This website provides information on beach water quality. MDPH produces an annual report that presents and summarizes beach water quality statewide. These reports can be found here.

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