Have you ever seen such a strange "blue beach"? Thousands of strange blue creatures have washed up on beaches on the US West Coast, leaving locals baffled.

This translucent little creature is called the sail jellyfish, also known as the "downwind sailor". They wash up all the way from Dana Point to Point Reyes National Seashore, and people are amazed by these little guys because it's a rare sight on the shore.

Sail jellyfish usually live far from the coast and rely entirely on wind to move. They are disk-like in shape and size and are very small carnivores. Sail jellyfish are a type of colonial polyp, and there are even some that are immobile, sedentary polyps.

Sail jellyfish are not fixed in one position. They use their protruding tops to sail on the water with the wind, so they are also nicknamed "downwind sailors". The sail jellyfish is light blue in color and feeds on zooplankton and other small sea creatures.

The movement trajectory of the sail jellyfish is completely determined by wind and ocean currents. When they wash up on the coast, they decompose and die. They turn gray, so big storms can be disastrous for sail jellyfish.

The sail jellyfish has spines on its body, but it is not dangerous to humans. Joe Mueller, a biology professor at the College of Marin, said in an interview: "When the numbers are low, the sail jellyfish will appear for a short time, maybe only a day or two. But when the numbers are high, they can last the entire season, You can see the whole beach is blue, like someone put grape jelly on the beach."

Sail jellyfish live in the northern hemisphere and move with the North Pacific Gyre winds, but strong winds can Get them off course.