Steer clear of these jellyfish to avoid a painful sting, Gloucester officials say

Gloucester officials are warning beachgoers to be on the lookout after lion’s mane jellyfish were spotted in the city’s outer harbor.

Officials issued an advisory for Niles Beach and nearby areas on Saturday.

“These jellyfish can deliver painful stings—even after they’ve washed ashore—so please use caution and avoid any jellyfish you may see,” the city’s advisory read. 

The lion’s mane jellyfish, considered a giant jelly, is “very toxic,” although there are few reports of human fatalities from the stings, according to the Monterey Bay Aquarium. They can grow to be more than three feet in diameter with tentacles longer than 100 feet, with the largest of the species typically found in Arctic waters. 

A nearly five-foot-wide lion’s mane jellyfish washed up in South Portland, Maine in June. 

Larry Madin, an emeritus scientist at the Woods Hole Oceanographic Institution, told The Boston Globe the jellyfish is “not as serious a jellyfish as a Portuguese Man O’ War.”

Still, he said, it’s best to keep your distance if you see one. 

“The tentacles with stinging cells can still sting as long as they’re still wet,” he told the Globe. “Don’t pick it up.”

Gloucester officials said they’ve reached out to the National Oceanic and Atmospheric Administration for guidance on dealing with large jellyfish. In the meantime, officials said they will keep people out of the water where jellyfish are present, post a warning flag if significant numbers are seen at Good Harbor Beach, and restrict access or close beaches entirely depending on jellyfish activity. 

“City staff are monitoring the situation closely this morning and will update as needed,” officials wrote. 

As of Wednesday, all Gloucester beaches were open.

Dialynn Dwyer is a reporter and editor at Boston.com, covering breaking and local news across Boston and New England.