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SAN DIEGO – Thousands of mesmerizing jellyfish have invaded the waters of Mission Bay and to the surprise of some swimmers, they didn’t get stung.

A group paddle boarding in Mission Bay encountered a moon jellyfish bloom in Mission Bay.

Tony Amicangelo, a travel photographer, was among the paddle boarders floating on the water near Mission Bay Sportscenter in Sail Bay in April. They discovered thousands of moon jellyfish floating under the surface of the water.

“We freaked out at first because we thought they stung. We almost called off our paddle board trip,” Amicangelo said.

Amicangelo said they were told they don’t often sting humans, and if they do it’s not often felt.

“Swimming with them was one of the most bizarre things I’ve ever done,” Amicangelo said.

The moon jellyfish is usually about 10 – 16 inches in diameter and can be recognized by its four horseshoe-shaped gonads in the center of the circular body.  They tend to have a six-month lifespan.

“As I was paddling out there was one jellyfish, five jellyfish, twenty jellyfish and then all of the sudden it was like a sea [of them] it was all white,” said paddle boarder, Sarah Rigby.

Moon jellyfish rarely sting humans, and if they do the impact is not normally felt.

“Moon jellies have a really weak sting so unless you get it in your mouth or in a cut you won’t even feel them,” said Vincent Levesque, a aquarist at the Birch Aquarium.

“We first start seeing them in January normally and they can last up through June or July, but it really depends on the food in the water column,” said Levesque.