Thousands of Blue Creatures Are Washing Up on Northern California Beaches. What Are They?

If you have been to Baker Beach in San Francisco or any stretch of coastline from Marin to Mendocino this week, you may have noticed something unusual: thousands of small, bright blue creatures covering the sand.

They are velella velella, commonly known as “by-the-wind sailors,” and their spring arrival along the Northern California coast is one of the more striking natural events you can witness without leaving the beach.

Despite their resemblance to jellyfish, velella velella are actually hydrozoans, a related but separate group of marine animals. Each one is a colony of tiny organisms that live together beneath a small, transparent sail that sticks up above the water. They float on the ocean surface and drift wherever the wind takes them. When spring winds shift direction, huge numbers get pushed toward shore and strand on beaches in massive blue carpets.

The creatures are not dangerous to humans. Their stinging cells are too weak to cause serious harm, though touching them with bare hands can cause mild irritation. The bigger concern is for dog owners. If pets eat them or roll around in a pile of them, it can cause gastrointestinal problems and skin or eye irritation.

Once stranded on the beach, velella velella dry out quickly and turn transparent and brittle, looking like small plastic candy wrappers scattered across the sand. They will decompose on their own and do not need to be removed.

This is not the first time the Bay Area has seen a major velella velella event. Mass strandings have been documented along the California coast for years, typically in the spring and early summer months.