OAK ISLAND, N.C. (WNCN) — This Labor Day weekend an island on the North Carolina coast warned swimmers about “dangerous” marine life in the surf.

The Oak Island Fire Department on Saturday had a special alert for jellyfish stings after several swimmers were impacted, officials said.

The island, located in Brunswick County near Wilmington, said that at least six swimmers were treated for injuries by beach patrols.

“No species has been identified, however, stings have been consistent with those of jellyfish,” the Oak Island Fire Department wrote in a news release.

The island used a purple flag — instead of a yellow or red flag — to denote “dangerous fish or marine life present in water.”

Oak Island Fire Dept. photo of a rip current rescue in mid-August, about three weeks ago.

Oak Island Water Rescue reported the flag color change to purple around 12:20 p.m. “due to numerous reported 🪼🪼🪼🪼🪼🪼stings.”

Fire crews said that beach-goers should swim with caution. Officials also added that the stings did not appear to be caused by Portuguese man-of-war, which have tentacles up to 30 feet long.

The rip current risk was low this weekend, according to the National Weather Service.