HAMPTON – The state has declared its Atlantic coastal waters and Hampton/Seabrook Harbor off-limits to shellfishing to protect the public from eating contaminated shellfish, state officials announced yesterday.

The state Department of Environmental Services and Fish and Game Department halted clam, mussel and oyster harvesting after finding unacceptably high levels of paralytic shellfish poisoning -- "red tide" -- in blue mussels at the Isles of Shoals and Hampton/Seabrook Harbor.

This year's red tide alert comes earlier than usual for Hampton Harbor, according to DES shellfish program manager Chris Nash.

"The toxin levels at the Isles of Shoals are not unusual for this time of year, but the toxin has shown up a bit earlier than usual at Hampton/Seabrook Harbor," Nash said.

New Hampshire shellfish dealers are taking the alert in stride.

"It happens every year," said Peter Tilton, owner of the Defiant Lobster Company in Hampton. "I just want people to realize it doesn't affect lobster."

Tilton, who sells lobsters, steamers and oysters, stipulated that the steamers consumers see in stores -- including his -- are safe because they come with a tag certifying they come from safe, open waters.

"All my clams come from Maine, and there's usually some area from Maine that's open, even in a bad year," Tilton said. "Maine has a huge coastline and red tide can be localized due to wind and current patterns."

Red tide hits when filter-feeding clams, oysters and mussels accumulate a powerful neurotoxin produced by a naturally occurring marine algae, according to a DES statement. The toxin is potentially fatal to humans, and cooking does not make contaminated shellfish safe.

Red tide happens in the spring, when the algae comes out of dormancy and blooms, Nash explained. Although the specific triggers are still being investigated, it is affected by water temperatures, rainfall, stormwater runoff and other factors, Nash said

While the past two years were less severe, a red tide bloom in 2005 was the most widespread and toxic on record for New Hampshire waters, Nash said. Meanwhile, the most recent case of Red Tide poisoning in the region happened last year in Maine when a fisherman consumed contaminated shellfish and "got very sick."

The latest closures will affect recreational shellfish harvesters and several aquaculture operations in the Granite State, Nash said.

►Click here for more on the status of shellfish waters from NH Fish and Game.

"Nobody in New Hampshire harvests wild stocks, but shellfish aquaculture operations will be affected," Nash said. "Some people grow blue mussels in Atlantic. They're not scheduled for harvest any time soon, but they'll need to sit tight and when red tide subsides and the shellfish purge themselves of it, they'll be fine."

"Two oyster operations in Great Bay may also be affected if this intensifies to the levels being seen offshore," Nash said. "But right now, the only people really affected are recreational harvesters."

Other New Hampshire shellfish harvesting areas, including the oyster beds around Nannie Island and Adams Point in Great Bay, were temporarily closed last week due to heavy rainfall, and will stay closed until more red tide and bacteria tests are done.

With red tide levels rising in both offshore and near-shore waters, it's too soon to know how severe this algae bloom will be or how long it will last, Nash said. Weekly sampling will continue from now until October.

"It's difficult to predict what will happen," said Nash. "These toxin levels could drop off next week, or they could get higher."