LEWES, Del. (AP) — More beachgoers have been getting an unexpected shock this summer as jellyfish numbers bloom along the Delaware coast, interrupting — but not stopping — the summer fun.

Beach patrol captains reported a dramatic increase in jellyfish activity and stings in July, the most they’ve seen in recent memory. Lewes Beach reported a fourfold increase in stings compared to 2024.

Lion’s manes, which can have 100-foot (30-meter) tentacles, sea nettles and moon jellyfish are some varieties that frequent Delaware’s summertime waters.

Jellyfish blooms have become common from Maine to Florida in recent years. Warming waters can create ideal conditions for jellyfish growth.

Normally, Delaware’s five state parks may report a handful of summer jellyfish stings, said Bailey Noel, a beach patrol captain. But Fenwick Island State Park recently reported 92 stings on a single July day. Three lifeguards were taken to urgent care after swimming in jellyfish-infested waters, Noel said.

The jellyfish at Delaware’s Towers Beach surprised Philadelphia resident Christina Jones, whose two daughters refused to wade back into the water after being stung, she said.

“The jellyfish are pretty bad,” Jones said. “And not only are they a lot in number, but they’re pretty big.”

Delaware State Beach Patrol started tracking jellyfish stings this year due to the rise in cases, said Noel. Most patrol teams do not track the data.

Lewes Beach Patrol treated 295 stings in 2024, the first year the data was collected, but reported over 1,200 cases so far in 2025, said Capt. Strohm Edwards. Lifeguards started carrying vinegar solutions, which can neutralize the venom agents, to help ease pain, he said.

But vinegar solutions may cause microscopic venom-coated barbs known as nematocysts to discharge, according to some research. Those experts recommend a baking soda slurry.

While venomous, stings from Delaware’s lion’s manes and sea nettles typically only cause minor irritation and pain, said Edwards. In cases of severe allergic reactions and symptoms — nausea, vomiting and trouble breathing — lifeguards can help.

Jellyfish blooms, sudden fluctuations in jellyfish populations, are not uncommon, said Gisele Muller-Parker, a retired marine biologist who would count dozens of lion’s mane jellyfish during her daily Lewes Beach walks in July. Temperature, salinity and food availability influence jellyfish breeding, and in favorable conditions, such as warmer waters, populations can explode.

“This year, we’ve never seen anything like this,” Muller-Parker said.

The jellyfish were near the end of their life cycle, finishing their reproductive phase and laying their eggs. Those jellyfish will die once water temperatures cool, said Keith Bayha, a research collaborator with the Smithsonian Institution National Museum of Natural History.

The jellyfish boom can harm ecosystems and marine industries, said Bayha, who has studied the animals for more than 20 years and helped identify a nettle species. Fish larvae primarily feed on plankton, but jellyfish can eat both the plankton and the fish. And with few natural predators, the jellyfish food chain is an ecological dead end, said Bayha.

Delaware’s boom this summer is far from alone. Florida’s Volusia County reported hundreds of stings around Memorial Day weekend. Gloucester, Massachusetts, reminded beachgoers to stay safe around jellyfish in mid-July. And in June, Maine’s Ogunquit Fire Department warned beachgoers about the increase in jellyfish after stings were reported.

Jellyfish research is limited, but Muller-Parker hopes more work will be done to assess the ecological ramifications of jellyfish blooms and improve safety advisories.

For now, some unlucky beachgoers will have to rely on home remedies and, in the case of Massachusetts resident Kathy Malloy-Harder’s third-grade nephew, a little bravery.

“When he got stung, he jumped up and started crying and said, ’I’m never coming back to the beach again ever,’” said Malloy-Harder, who had to try two stores to find vinegar for him. But she said that after talking about it “and once the sting subsided, he was interested in coming back and enjoying the beach.”

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Whittle reported from Portland, Maine.