Dramatic aerial video from AIR7 HD shows the lifeguards approaching the shark about 1:30 p.m. after ordering all swimmers out of the water.
The five lifeguards then pounced on the floundering shark and dragged it onto the sand.
No injuries were reported.
Lifeguards said two small thresher sharks came ashore, one at the Balboa Pier and the other in Corona del Mar at Inspiration Point. The shark in Corona del Mar was towed out to sea. Lifeguards removed the second shark and animal control officers euthanized it.
Lifeguards said both sharks were injured and close to death.
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"We looked over and I saw a fish, but I just ignored it and didn't think it was a shark," said one woman who was in the water at the time. "Next thing you know, I've got a woman yelling at me: 'There's a shark! There's a shark!'
"But I swear I felt that thing touch my leg -- the back of the tail," the swimmer said. "It was slimy."
Chris Lowe, a professor of marine biology and director of the Shark Lab at California State Long Beach, was shown video of the incident and said the shark appeared to be a juvenile thresher shark.
Sightings of thresher sharks are common in the area at this time of year, and people fishing from Balboa Pier sometimes catch them.
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