EPA’s Ambient Water Quality Criteria for Bacteria-1986 suggested states change their standards to reflect the results of research, which showed a correlation between high levels of E. coli and Enterococci with swimmer illnesses. The results also specified that E. coli was the most appropriate indicator organism for freshwater, while Enterococci were most appropriate for marine waters. As a result of these findings, New Hampshire changed its standards in 1988 to coincide with EPA’s recommendations.
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.)
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 (mL) of water in a single sample. The geometric mean standard for freshwater beaches is 47 counts of E. coli per 100 mL in at least three samples collected in a 60-day period. The standard at marine swimming beaches is 104 counts of Enterococci per 100 mL of water in a single sample. The geometric mean standard for marine beaches is 35 counts of Enterococci per 100 mL in at least three samples collected in a 60-day period.
When bacteria samples exceed the state standards a beach advisory will be posted by DES or a beach may be closed at the discretion of the town. Current advisories are updated as results become available, 24 hours after sample collection.