Red tide has hit Cape Ann and the North Shore, and all shellfishing is banned.

The state's Division of Marine Fisheries on Thursday banned harvesting of all softshell and razor clams on Cape Ann and the North Shore. That followed an announcement Wednesday that the harvest of blue mussels, carnivorous snails and whole sea scallops was prohibited because of elevated levels of paralytic shellfish poison toxin, also known as red tide.

It is still safe to swim, said Gloucester shellfish warden Peter Seminara, as this red tide is different from the type now plaguing Florida and killing fish and irritating beachgoers there.

"This is strictly a harmful bloom of another type," he said of the local red tide, a potent neurotoxin produced by a naturally occurring marine algae . "Filter-feeding shellfish ingest it and it gets concentrated in the meat."

Eating contaminated shellfish is potentially fatal to humans, and cooking does not eliminated the danger.

The red tide — and the shellfishing ban — extends from the New Hampshire border to the waters, tributaries and flats off Amesbury, Beverly, Boston, Danvers, Essex, Gloucester, Ipswich, Lynn, Manchester-by-the-Sea, Marblehead, Nahant, Newbury, Newburyport, Peabody, Revere, Rockport, Rowley, Salem, Salisbury, Saugus, Swampscott and Winthrop. The areas involved are N:1 through N:28.

Seminara said he does not know how long the red tide is sticking around.

"We're looking at a couple weeks at least," he said, depending on how the levels of the toxin rise or fall. Testing earlier this week showed higher levels in Essex Bay than in the Annisquam River.

Fried Essex and Ipswich clams are a specialty for local restaurants, and many, including Woodman's of Essex, have a fallback plan in case reserves run low.

The state is expected to retest for the toxin on Monday, Seminara said, and the results should be announced later in the week.

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