Red tide is high, and it's hitting local restaurateurs and shellfish harvesters hard. The New England coastline is seeing the worst red tide bloom in a decade this year, with coastal waters in Maine, New Hampshire and Massachusetts closed to shellfish harvesters.

"It's as bad as it's ever been," said Chris Nash, a red tide expert at the New Hampshire Department of Environmental Services. "We've seen the highest numbers that we've ever seen."

There are no commercial shellfish harvesting operations in New Hampshire, but Maine Gov. John Baldacci and Massachusetts Gov. Mitt Romney have declared an economic emergency for their states' shellfish industries, allowing them to receive federal aid. In New Hampshire, seafood restaurants have taken the brunt of the damage.

"It does have an effect because it's kind of negative publicity for seafood restaurants," said Paul Hartgen, president of the New Hampshire Lodging and Restaurant Association.

Brad Newick, co-owner of Newick's Seafood Restaurant in Dover, said this year's red tide bloom has affected him "maybe a little."

"It's such a scare, people sometimes think they're getting sick, but they don't realize that whatever red tide areas are affected, they're not digging clams there," he said.

Newick said he's received lots of calls from people inquiring about red tide, but "it hasn't shown big in the numbers." However, Newick said prices could increase even more if the red tide lingers throughout the summer season.

The prices he pays for clams have gone up about 10 or 20 percent, Newick said, because of the limited availability of clams. Newick gets his clams from northern Maine and sometimes Maryland. The federal ban on shellfish harvesting currently extends from the Schoodic Peninsula in Maine to southern Massachusetts.

Shellfish aficionados dining in area restaurants need only worry about high prices. According to Hartgen, consumers concerned about eating shellfish during a red tide outbreak should be aware that any shellfish served in a restaurant has been "tagged and inspected" and is from an area not affected by red tide.

An intense bloom in the ocean of microscopic algae causes red tide. The chief cause for concern during a red tide bloom are species of the phytoplankton Alexandrium, which contains a paralytic shellfish poison (PSP). Filter-feeding shellfish like clams and mussels ingest the algae, and the PSP can become concentrated in them. While it has no effect on the shellfish, humans ingesting shellfish containing the toxin can experience red tide poisoning, with mild symptoms that include numbness, tingling and burning of the lips. Severe cases of poisoning can result in respiratory paralysis and death, although such cases are extremely rare, Nash said.

The DES monitors PSP levels in shellfish. The minimum amount of toxin present for closure of shellfish beds is 80 micrograms of toxin per 100 grams of tissue. This year, levels peaked at between 800 and 900 micrograms, Nash said. Last week, levels came down to about 300 micrograms, but "it's not as though we're out of the woods yet. Three hundred is a very high number," Nash said. The bloom is particularly bad this year because of a series of storms that have pushed the algae further inshore than normal.

Once the weather gets warmer, Nash said the algae slow down reproduction, and the shellfish detoxify themselves. It's unclear how long it will take this year's red tide bloom to clear up.

"It could go all summer, but that would be unusual," Nash said. "It's really just a week-to-week thing right now."