These California Beaches Are Glowing Neon Blue At Night Here's Why

In San Diego, a red tide is making beach waters bioluminescent—as in, they are literally glowing in the dark.

This week, in a rare earthly occurrence, the waves of San Diego’s beaches are glowing neon blue. The natural phenomenon is taking both scientific theory and social media by storm.

“It kind of looked like the color of a light saber,” local photographer Stephen Bay, told CBS News. “It really was a bright blue color that was just fantastic to look at.”

The overwhelming indigo glow is caused by an algal bloom, also known as a red tide. But not all red tides light up at night. In a rare mixing of matters, the glow occurs only in the presence of bioluminescent phytoplankton—in this case, dinoflagellates—which light up on the faces of waves as they crash onto the shore. The illuminating results are truly an unmissable event for local Californians.

According to scientists, dinoflagellates flash blue in order to scare off their predators. “But any mechanical stress of sufficient magnitude, such as the forces in waves, surge, or by swimming animals (including us) can also trigger the luminescence,” explains the Scripps Institution of Oceanography.

Michael Latz, an expert in bioluminescence at Scripps, was the first to predict the phenomenon would occur this week. “The water contains dense numbers of dinoflagellates especially Ceratium falcatiforme and Lingulodinium polyedra…[which] is well known for its bioluminescent displays,” he told the San Diego Union-Tribune.

The last time San Diego had a major bioluminescent occurrence was in 2011, although there was some mild glowing in 2013. So far, the ocean has been lighting up since Monday, from the beaches in La Jolla to Encinitas in North County. However, it is impossible to gauge how long it will last.

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“We can’t predict when these things occur, we don’t know how long they will last, when they’ll be here, and we really don’t understand the dynamics,” Latz told the Union-Tribune.

The bioluminescent glow could last for a week or up to a month, but aspects of it from all angles remain an earthly mystery. For those in San Diego, the best time to witness it is about two hours after sunset. While bioluminescent surf is rare in San Diego, there are places around the world, such as Puerto Rico’s Mosquito Bay, where the phenomenon can be observed year round.