New Hampshire analyzes swimming water for indicator organism to protect public health at beaches. E. coli is the most appropriate organism for freshwater and Enterococci are most appropriate for marine waters.
The Beach Program also collects cyanobacteria samples observed at beaches in order to identify possible cyanotoxins. Certain species of cyanobacteria produce harmful toxins that can cause illness in animals, including humans, if ingested in large quantities, or upon contact with the skin or mucous membranes (See Health Risks Associated with Toxic Cyanobacteria.)
State Standards and Advisories
New Hampshire law (RSA 485-A:8) provides standards for the state’s water quality. The standard at freshwater swimming beaches is 88 counts of E. coli per 100 milliliters of water (counts/100 ml) in a single sample. Beach advisories are issued at freshwater beaches when either two samples taken at a beach exceed the standard or when one sample exceeds 158 counts/100 ml.
The New Hampshire standard at marine swimming beaches is 104 counts of Enterococci per 100 mL of water (counts/100 ml) in a single sample. Beach advisories are issued at coastal beaches when either two samples taken at a beach exceed the standard or when one sample exceeds 174 counts/100 ml.
The New Hampshire standard for cyanobacteria is either cyanobacteria making up 50 percent of the total cell count or having a cyanobacteria cell count greater than 70,000 total cells per ml of water. Beach advisories are issued when samples taken from scum at a beach are either more than half cyanobacteria cells or the cell concentration is greater than 70,000 cells per ml of water.
When bacteria samples exceed the state standards a beach advisory is posted by DES. A beach may be closed at the discretion of the town. Current advisories are updated as results become available, 24 hours after sample collection.