The sea nettle is a common jellyfish seen on the East Coast during the summer. It's usually confined to brackish, warm waters, according to the Virginia Institute of Marine Sciences (VIMS).
That may explain why it's showing up in North Carolina rivers.
Reports have come in of sea nettles spotted in the Neuse River near Oriental and the Pamlico River near the intracoastal waterway, according to environmental nonprofit, Sound Rivers.
The tentacles of sea nettles are covered in stinging cells called nematocysts, which stun or kill their prey, according to the Chesapeake Bay Foundation (CBF).
The sting can be treated with vinegar, which can keep nematocysts from stinging.
A sting can cause a painful rash that lasts about 20 minutes, Sound Rivers said, but some people can have worse reactions.
The sting of a sea nettle is moderate to severely painful, but isn't dangerous unless there's an allergic reaction, according to VIMS. The South Carolina Department of Natural Resources says it can feel more like burning than a sting.
Hundreds of people are stung by sea nettles in Hilton Head, South Carolina every day, according to The Island Packet. They're the most common case of jellyfish stings in South Carolina coastal waters.
Adult sea nettles can have a bell up to 8 inches in diameter, with about 24 tentacles that can be several feet long, according to VIMS.
Sea nettles in lower salinity are usually white or yellow in color. In water that has more salt, they can be reddish and brown, according to VIMS and Sound Rivers.
The small jellyfish graze on zooplankton, small fish, worms, other jellies and crustaceans and keep the populations of some smaller animals from growing out of control, according to CBF.
While sea nettles can swim, they are mostly born about by the wind and currents.
Sea nettles help protect the oyster population by eating other jellyfish that prey on oyster larvae.
Sea nettles have few natural predators, but healthy sea turtle and fish populations help control the jelly population, according to CBF.