NAHANT (CBS) — Thinking about hitting the beach this weekend? Watch out for the giant jellyfish.

“The Department of Conservation and Recreation (DCR) is warning the public of the presence of lion’s mane jellyfish at Nahant Beach in the Town of Nahant,” a recreational advisory from the state issued Friday reads. “Additionally, the agency has posted purple flags at the beach, which indicate the presence of dangerous marine animals.”

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According to the Smithsonian, the lion’s mane jellyfish is among the largest of the jelly species, stretching up to 120 feet across. Their tentacles “contain large amounts of neurotoxins that can cause a range of effects when humans come in contact, from a rash to affecting respiratory function,” the institution says.

Humans don’t usually come into contact with the jellyfish because they are more commonly found in the open ocean, but swimmers should keep an eye out.

“This particular year we’ve seen a huge number of them and a lot of them are getting really close to the beaches,” said Chris Doller of the New England Aquarium. “A lion’s mane jellyfish can have as many as a thousand or more tentacles and each one of those tentacles can pack a pretty good punch.”

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Doller says the average lion’s mane is much smaller though – about the size of a dinner plate. But even a tentacle that breaks off – can keep stinging for a while.

“Most people don’t have a severe reaction to a jelly sting but as we know even with bee stings some people are really sensitive to those types of animals,” Doller said.

If stung, vinegar can take some of the pain away. Doller says swimmers should be on the lookout through September.

“I would highly discourage from swimming when you see them near a beach. You want to keep your distance. Come to the aquarium and see them in a safer way,” he added.

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The DCR said it is not aware of the jellyfish at any location other than Nahant Beach Reservation. Warning flags are being posted at King’s Beach in Lynn as a precaution.