Courtesy of Tiffany Booth/Seaside Aquarium

Images of a previous years' event show countless velella velella on a north Oregon coast beach.

The end of spring on the Oregon coast brings three reliable sights: great weather, throngs of tourists and “blue tide.”

The tide is made not of water but of countless blue creatures called velella velella, which wash ashore in droves this time of year. The Oregon Coast Aquarium announced Friday that the jelly-like organisms have already arrived on Oregon beaches, in some places covering the sand in a carpet of blueish purple.

Visitors should expect to see them for the next few weeks, the aquarium said, though they’ll soon begin to decay and turn translucent, creating a foul smell on the beach.

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Jamie Hale/The Oregonian

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Courtesy of Tiffany Booth/Seaside Aquarium

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Also known as “by-the wind sailors,” the jelly-like organisms utilize clear, triangular sails to travel across the surface of the ocean, drifting where the breeze takes them. While they always aim to be blown away from shore, stronger winds in spring and summer months tend to strand them on land.

Velella velella were originally classified as a jelly, but researchers have since recognized the creature as a unique species of hydrozoan, a class of predatory salt water animals. The tiny sailors are found in every ocean on the planet and have no independent form of movement.

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Courtesy of Tiffany Booth/Seaside Aquarium

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Jamie Hale/The Oregonian

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Each apparent individual is actually a complex colony of all-male or all-female polyps, connected by a canal system that transports food and waste. As they drift across the surface of the ocean they feed on plankton, stinging them with barb-tipped cells inside their tentacles.

The venom is generally too weak to pose a threat to humans, but the aquarium cautioned beach-goers from touching the velella velella – or any jelly-like creatures for that matter – as some people have a stronger reaction to the venom than others.

--Jamie Hale | jhale@oregonian.com | @HaleJamesB

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Terry Richard/The Oregonian

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Jamie Hale/The Oregonian

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Courtesy of Tiffany Booth/Seaside Aquarium

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