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New Hampshire Department of Environmental Services

Frequently Asked Questions
  • What does cyanobacteria look like? Can I swim at the beach if it is present?
    A cyanobacteria bloom can appear as a blue-green scum or as dispersed cells floating either on the surface or suspended in the water column. Cyanobacteria occur naturally in waterbodies throughout the world. However, when excess nutrients enter the water, cyanobacteria cell concentration may increase. Once a bloom or surface scum forms, cyanobacteria can present a potential health risk to humans and pets. NHDES advises against swimming in any waters experiencing a cyanobacteria bloom, and pets and children especially should not make contact with the water.
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  • What should I do if I suspect a cyanobacteria bloom?
    If you suspect a cyanobacteria bloom make sure that children and pets do not drink, wade, swim, or make contact with the water. Call the NHDES Cyano hotline to report the bloom at (603) 848-8094. If you are able, collect a water sample with a clean bottle or Ziploc bag while wearing gloves. Label the container with location, date, time and your contact information. Place the sample on ice until it can be transferred to the NHDES Limnology Center for microscopic analysis. If you are unable to collect a sample, a picture of the bloom can also assist limnologists with identification. The NHDES beach program will post an advisory for the beach area if necessary.
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  • How can a cyanobacteria bloom be removed or controlled?
    The only way to decrease the likelihood of a cyanobacteria bloom is through continued watershed management practices that reduce nutrients to the water. Assess your surroundings and your habits. Be aware of the Shoreland Protection Act and its requirements for use of fertilizers along the shoreline. No fertilizer, except limestone, may be used within 25 feet of the reference line (shoreline). Limestone, low phosphate or slow release nitrogen fertilizer can be used above this point. Pick up after your pets and be aware of the potential for septic systems to fail.

    A bloom can last anywhere from a few days to a few months. Pay attention to the changing conditions of your individual shoreline for the possibility of a bloom.

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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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