M Street Beach (@M Street) is sampled weekly from May 30th from September 1st.

Water quality at Boston beaches is tested local municipalities or by the Department of Conservation and Recreation (DCR) with assistance from the Massachusetts Water Resources Authority. Beaches in Boston are tested on a daily or weekly basis.

Testing frequency depends on how likely the beach is to have water quality issues. Infrequently used beaches or beaches that historically have had very few, if any, water quality issues are tested less often, while high-use or historically problematic beaches are tested more often. Detailed information on testing frequency is made available in the information listed for a particular beach.The water at marine beaches is tested for the presence of Enterococci, a group of bacterial species typically found in human and animal intestines and are therefore present in sewage. Enterococci is also referred to as indicator organisms. Indicator organisms are used to predict the presence of pathogenic, or disease-causing, organisms associated with fecal contamination. Swim Guide checks for the latest information daily, Monday - Friday during the swimming season. A beach is marked Green when less than 104 units of Enterococci / 100 ml of water is present in a single sample, or when the geometric mean of 5 samples contains less than 35 units / 100ml of water.A beach is marked Red when more than 104 units of Enterococci / 100 ml of water is present in a single sample, or when the geometric mean of 5 samples contains more than 35 units / 100ml of water.A beach is marked Grey when there is no current or reliable monitoring information available.