Though state waters around the Vineyard, Nantucket and south and east of Cape Cod remain clear of red tide, the state late last week as a precautionary measure closed federal waters to shellfishing. These are waters that are more than three miles from shore.

Red tide is a toxic marine algae that when ingested by shellfish that makes them harmful for human consumption. A bloom of algae in the Gulf of Maine has caused the closing of shellfish beds for the waters north of Cape Cod. The bloom is believed to be expanding and the state action is being taken as a precautionary measure.

The closure has no impact on shellfish harvested from state waters near the Vineyard. Fish markets and commercial shellfishermen already are well aware of the closed areas.

The closure affects the harvesting of surf clams, ocean quahaugs and mussels and carnivorous snails and the landing of whole sea scallops.

According to a prepared statement released by the state, “This emergency action restricts vessels registered under the laws of the commonwealth fishing in federal waters from taking or possessing for commercial or recreational purposes prohibited species and products.”

Lisa Capone, a spokesman for the state Executive Office of Energy and Environmental Affairs, said yesterday, “We are continuing to sample federal as well as adjacent state waters.”

More information on red tide and the closure is available by visiting the Web site of the state Division of Marine Fisheries.