Beachgoers spotted bright blue, glowing waves in Southern California’s coastline this week.

The bioluminescent waves, which turn the ocean red during the day and glow neon blue night, have been reported being seen at multiple California city coasts including Newport Beach, Laguna Beach, Oxnard, Malibu, and Diego coastlines over the past week.

“Some years have been better but this year, so far at least this week, has had pretty bright bio[luminsecent]” said nature photographer Mark Girardeau, who runs the website Orange County Outdoors.

"At Main Beach they have some pools that fill up in the sand during high tide and then the water just sits there once the tide goes down. And then if you go walk in, it just lights up super bright."

Girardeau, who works at a whale watching boat in Newport Beach, noticed on Sunday the ocean appeared a brown red color during the day and later learned his instincts were right that the bioluminescence returned. Having documented the glowing waters annually since the 2020 super bloom, he and his fellow photographer partner Patrick Coyne did not hesitate to capture more stunning images.

Girardeau shared photos and video on his website and social media platforms.

"I was freaking out because I've never seen this before. I thought it was just a super rare phenomenon," Girardeau said. "It was like super bright."

How does bioluminescence make waves glow at night?

Bioluminescence, a chemical reaction most commonly seen in marine organisms, causes light to emit from living things. When these organisms are moved by waves or the paddle of a kayak or canoe, the light becomes visible. Most marine and land organisms' bioluminescence appears blue-green, however, some land species, such as fireflies, beetle larvae, and even mushrooms, also glow yellow.

What species cause bioluminescence waves?

High densities of Lingulodinium polyedra (L. polyedra), a plankton species recognized for the neon blue glow it emits, causes the spectacle, according to a 2020 report by UC San Diego’s Scripps Institution of Oceanography and Jacobs School of Engineering.

The species is a type of dinoflagellate, a single-celled organism with two flagella. Dinoflagellates and diatoms are the two main types of phytoplankton classes, according to the National Ocean Service.

Phytoplankton are an essential part of making the planet livable as they contribute to the global carbon cycle as key producers of oxygen.

Phytoplankton can grow explosively over a few days or weeks, according to NASA.

Watch:Florida kayaker captures video of dolphin swimming in bioluminescent waters for its food

When and where can I find bioluminescence?

The best times to see bioluminescence are in the summer and fall on dark, cloudy nights before the moon has risen or after it sets, according to the National Park Service. 

Phytoplankton blooms occur in the Gulf of Alaska thanks to the nutrient-rich water that provides fertile conditions for species, according to NASA.

Notable spots to see bioluminescence in popular bodies of water in the U.S. include Tomales Bay State Park in northern California, Vieques National Wildlife Refuge in Puerto Rico, Olympic Coast National Marine Sanctuary in Washington and bays near Acadia National Park in Maine. The phenomenon can also be seen anywhere along the National Seashore's coastline, according to the National Park Service.

Girardeau recommends checking out a couple of beaches where they have been reported and staying at each one for a while to determine whether they're visible.

What's the best way to see bioluminescence at the beach?

Girardeau said you have to let your eyes adjust to the bioluminescence as waves some nights only have a faint glow. He also recommends practicing patience.

"We get messages all the time from people saying they went down on the beach and stood there for like five minutes and didn't see it and they just left," Girardeau said. "You have to hang out there for a while because it depends on the sets."

The higher the tide the less noticeable the glow is, Girardeau added. He also said that while he's definitely seen the glowing waves shortly after sunset, he notices they are more noticeable after midnight.

Is it safe to swim in bioluminescence?

Lingulodinium polyedra can produces yessotoxin, a compound that acts as a neurotoxin, in some locations the Mediterranean. However local populations do not produce yessotoxin, according to the 2020 UC San Diego’s report.

"However, some people are sensitive to inhaling air associated with the red tide, so the organisms must be producing other compounds that can affect human health," the report said. "In general, during a red tide there is lots of dissolved and particulate matter in the water with associated enhanced microbial activity. It is personal choice whether to go in the water, but there is no public health warning associated with the red tide."