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New Hampshire Bans Offshore Shellfish Harvesting During Intense Toxic Algae Bloom

The state is temporarily banning shellfish harvesting in coastal Atlantic waters because of a severe bloom of potentially toxic algae.

The ban applies to mussels, clams and oysters in near-shore and offshore waters. It does not apply to lobsters, or to inland areas, such as Great Bay and Little Bay.

The advisory also does not indicate a threat to swimmer or surfers, who were allowed back onto the Seacoast beaches as of Monday.

Credit Dan Tuohy / NHPR
A lifeguard keeps watch at Jenness State Beach in Rye after the park began to reopen this week. Shellfishing in this and other coastal areas like is temporarily prohibited due to an intense algae bloom.

The Department of Environmental Services says the ban comes out of an abundance of caution, after recent seawater tests showed extremely high levels of marine algae capable of producing a neurotoxin that can build up in shellfish.

The state has not found the neurotoxin in any shellfish yet, but testing will continue through next week.

People who ingest the toxin in shellfish can develop what’s called amnesic shellfish poisoning, which can have gastrointestinal effects and sometimes lead to neurological damage or death.

Officials say the toxin is considered a threat when algae concentrations are above 15,000 cells per liter of water. The state’s previous high concentration was 40,000 cells per liter. Last week, tests off Hampton and Seabrook showed more than a million algae cells per liter of seawater.

DES says neighboring states are also seeing high levels of these algae, but not as high as New Hampshire’s. They’re still studying what might be causing the bloom to be so intense.

This story has been updated with photos of the algae sampling process provided by DES. 

Annie has covered the environment, energy, climate change and the Seacoast region for NHPR since 2017. She leads the newsroom's climate reporting project, By Degrees.
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