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Beaches in San Diego are lighting up blue: Here’s why

From La Jolla to Encinitas, people are sharing incredible photos.
From La Jolla to Encinitas, people are sharing incredible photos. From La Jolla to Encinitas, people are sharing incredible photos.

San Diego beaches are lighting up blue due to a phenomenon called a red tide.

People have been sharing photos of the blue light, called bioluminescence, in waves crashing on to beaches. On this occasion, it is caused by a bloom of phytoplankton brought by the natural phenomenon known as the red tide.

Bioluminescence expert Michael Latz, a scientist at Scripps Institution of Oceanography at UC San Diego, explained the red tide phenomenon.

“The red tide is due to aggregations of dinoflagellates including Ceratium falcatiforme and Lingulodinium polyedra, the latter of which is well known for its bioluminescent displays, with waves or movement in the water causing the phytoplankton to glow neon blue at night.”

Phytoplankton are microscopic, single-celled plants that occur naturally in some coastal waters.

During the day, the phytoplankton rise to the surface to capture sunlight for growth and reproduction. As they contain a reddish pigment, they make the sea appear red during daylight hours.

Latz says the best time to view the blue display is from a dark beach at least two hours after sunset.

the blue side of red tide

A post shared by Ben Guenther (@bengrulz) on

The last red tide in this area occurred in September 2013 and lasted one week. The one before that, in October 2011, lasted a month.