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New Hampshire Department of Environmental Services

FAQs – Closures
  • What causes a closure?
    Waters documented as polluted through the sanitary survey are closed to harvesting, or may be "conditionally approved" during dry weather when the pollution only occurs from surface water runoff resulting from rainstorms or snowmelt. High bacteria levels in the shellfish growing waters indicate the presence of human or animal waste, and shellfish exposed to this contaminated water can cause illness if consumed by people. Sources of bacteria include malfunctioning, improperly installed, or poorly maintained septic systems, municipal and industrial discharges of wastewater, illegal sewage discharge from boats, waterfowl and wildlife wastes, and polluted stormwater runoff.
    Rainfall can cause temporary shellfish bed closures because rainwater runoff often transports high levels of pollution into the shellfish growing waters. Some waterbodies can only assimilate small amounts of rainfall/runoff before they become polluted, while other waterbodies can handle larger rainfall events and still be safe for shellfish harvesting.
    Shellfish beds are closed when they are subject to accidental releases of untreated sewage or hazardous materials such as petroleum products.
    Beds in close proximity to wastewater treatment plant outfalls and marinas are permanently closed.
    Areas where no sanitary survey has been conducted are closed as a safety precaution. These waters are designated as "unclassified." Additionally, if the sanitary survey is not kept current through mandatory three-year updates, the area must be closed.
    Incidences of "Red Tide," which can cause Paralytic Shellfish Poisoning, will also cause closures. Red tide is caused by "blooms" of microscopic algae which produce a potent neurotoxin. When these algae populations reach high densities, the toxin can be concentrated in shellfish, which in turn pose a potential health risk to shellfish consumers. Once levels of toxin in shellfish reach an established threshold, shellfish harvesting is stopped in affected areas.
    Some shellfish beds are closed for resource conservation for some or all of the summer.
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  • Why does rainfall close some shellfish beds?
    Rains can cause temporary shellfish bed closures because stormwater runoff is known to transport pollution into surface waters. Pollutants come from feces (humans, animals, and birds), boats and marinas, industrial and farm use (e.g., pesticides, plastics, detergents, oil, and gasoline), industrial effluents and surface runoff (e.g., acids, caustics, salts, and metals), and road and highway runoff. Some shellfish beds will be closed after a rainfall event until adequate flushing of the shellfish growing areas has occurred and the shellfish themselves have had a chance to purge themselves of pathogens.
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  • Does a snow storm warrant a closure?
    A snow storm (without any form of rain) does not warrant a closure, because such storms do not produce significant runoff. A closure may be instituted if a snow storm occurs with rain, or the snow accumulation quickly melts and causes polluted runoff.
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  • How long do the beds remain closed after a rainfall closure?
    Shellfish beds remain closed until there has been adequate flushing of pollutants from the affected waterbody, and the shellfish have had adequate time to purge themselves of contaminants. The amount of time that shellfish beds will remain closed is 14 days after the rainfall event, or sooner if water and shellfish tissue samples show that harvesting conditions are once again safe. In recreationally-important areas such as Hampton/Seabrook, NHDES usually conducts water and meat sampling to determine if the closure can be lifted sooner than the typical 14-day period.
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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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