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New Hampshire Department of Environmental Services
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Health Risks

What are Indicator Organisms?

Indicator organisms are used to measure changes in water quality and the potential presence of hard-to-detect disease-causing organisms also called pathogens.

Indicator organisms provide evidence of the presence of a potential disease-causing organism that survives under similar physical, chemical, and biological conditions.

Indicator organisms are easy to detect using simple laboratory tests; results are available within 24 to 48 hours. They generally are not present in unpolluted waters and appear in concentrations that can be correlated with the extent of contamination. The die-off rate is similar to the die-off rate of the pathogens of concern.

E. coli is the indicator organism for freshwater beaches. Enterococci are the indicator organisms for marine beaches.

Health Risks Associated with Bacteria, Protozoans, and Viruses

Photo of bacteria dishNote: While there are rarely reported cases of illnesses associated with swimming water in New Hampshire, the DES Beach Program wants the public to be aware of the possible health risks.

When disease-causing organisms are present at swimming areas, they pose certain health risks. The possibility exists that any person who ingests or has contact with contaminated water may become ill. Symptoms associated with an illness depend upon the organism present.

These organisms, including bacteria, protozoans, and viruses, can cause a variety of illnesses.

Here is a brief list of some common organisms with their associated illnesses and symptoms.

  Pathogen Illness Symptoms
Bacteria Escherichia coli Gastroenteritis Vomiting, diarrhea, death in susceptible populations
Salmonella typhi Typhoid fever High fever, diarrhea, ulceration of the small intestine
Vibrio cholerae Cholera Extremely heavy diarrhea, dehydration
Protozoans Cryptosporidium Cryptosporidiosis Diarrhea
Giardia lamblia Giardiasis Mild to severe diarrhea, nausea, indigestion
Entamoeba histolytica Amoebic dysentery Prolonged diarrhea with bleeding, abscesses of the liver and small intestine
Viruses Hepatitis A and E Infectious hepatitis Jaundice, fever
Calciviruses (Norwalk- and Sappro-like viruses) Gastroenteritis Vomiting, diarrhea
Adenovirus Respiratory disease Eye infections, diarrhea

Health Risks Associated with Toxic Cyanobacteria

Photo: Cells of MicrocystisAn increase of nutrients to a waterbody is part of the aging process of lakes known as eutrophication Adobe Acrobat Reader Symbol(Fact Sheet BB-3). An increase of phosphorus in combination with increased sunlight and warmer water temperatures often accelerates the production of cyanobacteria (blue-green algae) growth in the lake. Biologists are most concerned when cyanobacteria scums wash up on public beaches.

Several cyanobacterial species produce toxins (cyanotoxins) that can cause both acute and chronic problems in humans. However, there have been no documented cases of cyanotoxin-related illnesses in New Hampshire. Acute effects, such as skin and mucous membrane irritations, can occur after short term exposure with water containing these toxins. Chronic effects, such as liver, kidney, and central nervous system damage, can occur over a period of time from ingestion of water containing large amounts of toxins. Some individuals are at greater risk of injury due to these toxins, including children and immuno-compromised individuals. Domestic animals and livestock are also at risk of illness or death if large amounts of toxin-producing cyanobacteria are ingested.

Photo of a cyanobacteria scumDES will collect cyanobacteria scum samples throughout the swimming season. Samples that are positively identified as toxin-producing cyanobacteria species will be further analyzed for toxins.

In the event that a person or animal has come in contact with water contaminated by cyanobacteria, he or she may experience one or more of the following symptoms:

Headaches, nausea, diarrhea, abdominal pain, vomiting, and itchy, irritated eyes and skin

The University of New Hampshire is currently conducting research on cyanobacterial species in New Hampshire lakes, streams, and the Great Bay Estuary.




NH Department of Environmental Services | 29 Hazen Drive | PO Box 95 | Concord, NH 03302-0095
(603) 271-3503 | TDD Access: Relay NH 1-800-735-2964 | Hours: M-F, 8am-4pm

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