The warm El Niño waters may have played a part in bringing an unexpected swimmer that was recently caught on video to the Long Beach coastline, an expert said.

Diver Roger Hanson recorded a Pacific seahorse swimming in about 4 feet of water below Alamitos Bay this past Sunday, the Long Beach Press-Telegram reported.

“I was shocked because I know that that’s a once in a lifetime moment,” said Hanson, who told KTLA he has completed more than 5,000 dives, and even swam with Jacques Cousteau at the Great Barrier Reef.

Hanson said he spotted a Pacific seahorse once before — in January — but didn’t have his camera with him.

“So Sunday I went out and I go ‘You know what, I’m going to bring my camera,’ and there it was,” said Hanson, who provided video of the encounter to the Press-Telegram and later to KTLA.

The sighting was indeed uncommon, according to Sandy Trautwein, the curator of fish and invertebrates at the Aquarium of the Pacific.

More and more unusual creatures are likely being brought to the Southern California coast due to the warmer waters being created by this year’s El Niño conditions, Trautwein said.

“We have a very unusual event that’s been going on for the past year or so at least, where the waters are at higher than average temperatures,” Trautwein said.

At least three “highly venomous” sea snakes have washed up on Southern California beaches since mid-October, when the first yellow-bellied sea snake to appear in the region in 30 years was spotted in Oxnard.

Last June, thousands of small crabs washed up on beaches in Orange and San Diego counties.

The crustaceans, native to the waters off Baja California, often appear in El Niño years.

In addition to the El Niño conditions, a huge area of unusually warm water in the Pacific known to scientists as “The Blob” could have led the Pacific seahorse and other sea life to Southern California waters.