California beachgoers turned to social media this week to post photos online depicting thousands of blue sea creatures washing ashore  — a phenomenon scientists say they haven’t seen in about a decade.

According to experts, it’s likely the large colony of creatures, known as Velella velella, turned up on the San Fransisco shoreline this week because of strong winds.

The blue-tinted creatures float on the sea with their sail-like tops and are commonly referred to as the “by-the-wind sailor,” according to the Scripps Institution of Oceanography. Their diet consists of Zooplankton and fish eggs.

Still, it’s something scientists haven’t seen in quite some time and, as KNTV noted, it’s unclear exactly why they are turning up so late in the summer since they usually bloom around April or May.

“It’s been eight years, plus or minus, that we’ve seen them,” Monterey Bay Whale Watch marine biologist Nancy Black told the Santa Cruz Sentinel. “Why they’ve come now, it’s hard to say.”

“It’s a little bit out of whack,” Rich Mooi, curator of invertebrate zoology and geology at the California Academy of Sciences, added to the Los Angeles Times.

It’s estimated that thousands, if not millions, of the creatures turned up on the California shores this week, prompting beachgoers to turn to social media and post photos.

Experts say they pose no threat to humans.

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