Every year during the summer or fall, shore waves across the Bay Area are lit up with flashes of beautiful blue light.

This beautiful blue light is caused by millions of tiny bioluminescent plankton called dinoflagellates. But how do these minuscule organisms produce such a dazzling display?

Keep reading for the facts about the science behind bioluminescence, and where you can see it for yourself in the Bay Area.

• Jump straight to: How you can see bioluminescence for yourself in the Bay Area

How do organisms make light?

Bioluminescence is a chemical reaction that happens inside many organisms, from bacteria to squid, shrimp, fungus, fireflies and even starfish.

This is all thanks to a light-emitting molecule in their cells called luciferin, combined with a photo protein called luciferase. This protein creates the chemical reaction between luciferin and oxygen, making these organisms glow.

Different forms of luciferin can produce different colors of light. Fireflies, for example, have a form of luciferin in their cells that emit green light, whereas marine organisms like the dinoflagellates found around the shores of the San Francisco Bay emit blue light.

Why do some organisms produce bioluminescence?

Some species of bioluminescent sea creatures, like some jellyfish, have evolved to become bioluminescent due to their diet. When they eat other bioluminescent organisms, they borrow that chemical that allows them to produce light within their bodies.

Other sea creatures, like angler fish that have that ball of light that glows and lures in prey, and flashes light to repel predators, get their bioluminescence from a certain bacteria called photobacterium.

“And the standard rule of thumb is that, what glows in the ocean attracts and what flashes repel,” said Steve Haddock, a senior scientist at Monterey Bay Aquarium Research Institute who researches bioluminescence organisms. He also runs a citizen science website, JellyWatch.org.

Bioluminescence is a terrific deterrent against predators that would eat these organisms. It also functions like a flashlight for finding and attracting prey. Some organisms use their glowing abilities as camouflage — they turn light on to block out their silhouette, a kind of cloaking device — hiding them from potential predators.

What are dinoflagellates? And how are they related to red tides?

Dinoflagellates are single-celled phytoplankton that are usually invisible to the naked eye. But when they are present in high numbers, they can turn the water a hazy green or even orange, depending on the pigments present in cells of that species. When left alone, dinoflagellates won’t produce any light, but when things like ocean waves, wind, and sea creatures disturb them at night, they become bioluminescent, dazzling with a blue light.

When water temperatures and conditions are just right, blooms of dinoflagellates can grow rapidly and accumulate in high concentrations, causing an event known as a red tide. Red tide is a term generally used to describe when phytoplankton or algae becomes so abundant that it discolors the water, sometimes appearing orange or red.

“So you get a red tide in the daytime and blue tide in the nighttime,” said Haddock.

Can I swim or kayak in bioluminescent waters caused by a dinoflagellate red tide?

A red tide of dinoflagellates is not to be mistaken with the harmful red tides that killed many fish across the Bay Area recently. The species that caused that red tide is called Heterosigma akashiwo, and although classified as not dangerous to humans, this species can suck up all the oxygen that fish need in the water, causing them to die.

Most of the bioluminescent species of dinoflagellates are not dangerous to humans. And it should be fine to kayak or swim in bioluminescent waters, says Haddock. But during a red tide, when the water is murky brown, multiple species of different organisms may be present, including the ones that release toxins that might be harmful to humans and animals.

Some species of dinoflagellates can produce various toxins, and their decomposition releases the toxin into the water, and it can even enter the air and become a problem for marine animals and humans, according to Peter Roopnarine, a curator of geology at California Academy of Sciences.

“Pay attention to your local advisories about water quality, and things like shellfish poisoning,” Haddock advised.

The rule of thumb is: If the water is a murky brown instead of the usual green or blue, it’s best to stay out of the water. Read more about the algal blooms during the red tide in the Bay Area here.

When can I see bioluminescence around the Bay Area?

Johnny Chien, a hobbyist photographer and Bay Area resident recently captured bioluminescence at Seacliff State Beach and Manresa State Beach in Santa Cruz County. He says that when looking for bioluminescence, patience is key.

“It’s one of those natural [phenomena] that is kind of like the Northern Lights,” said Chien. Chien says that because the wind and tide play important roles in the movement of these bioluminescent planktons, it’s worth it to walk around and explore the beaches when you’re out looking for them. “You could have combinations where there are blotches or certain parts of the beach that are active, certain parts are not,” said Chien.

What time of year is best to see bioluminescence?

Bioluminescent planktons are around all year long in our California waters. But it’s only when there’s a high concentration of them that makes for a big bioluminescence event, says Haddock. And the best time to see one of those is usually from June until October.

Predicting a big bioluminescent event is not easy. It depends on many factors like temperature, the weather, wind, and tide. So with that in mind…

Tip #1: Watch the weather

Phytoplanktons like dinoflagellates can reproduce significantly in optimal warm temperatures. Very often, these warm temperatures can cause an increase in dinoflagellate populations, said Roopnarine.

Haddock says that spotting bioluminescence is “best in the fall,” especially on a balmy day in late summer, “where it’s been relatively warm and calm.”

Sometimes conditions occur that lead to massive increases in abundance. These can be seasonal causes, when currents concentrate them in some areas, or when nutrient conditions become very favorable for population increase among bioluminescent planktons, said Roopnarine.

A rainy or windy day followed by a calm day can kick off the sequence of events leading to a bloom. Rainy days will bring nutrients like phosphate and nitrate found in fertilizers used on land into the watershed and eventually into the sea. Wind will cause the mixing of deeper water, which has more nutrients, up to the surface, said Haddock.

Calm waters in a bay where the area is more enclosed and unaffected by the wind, could be a great spot to look for them after a windy or rainy day, said Haddock.

Tip #2: Look for red tides around surf zones

Shreenivasan Manievannan, a professional photographer in the Bay Area, captured a video of the bioluminescence last year in Pacifica when he noticed the red tide event earlier in the day.

“I noticed a distinct change in [color in] the waves in the surf zone,” said Manievannan.

• Tell us: What else would you like to read a guide about right now?

Tip #3: Track those dinoflagellates (or follow those who do)

You might also be able to track dinoflagellates on iNaturalist, a crowdsourced species-identification system.

Also, stay tuned to local aquariums like the Monterey Bay Aquarium and social media updates on bioluminescence events.

Tip #4: Consider the visibility

For the best visibility, catch the bioluminescence on a moonless night or a night during a new moon.

“The darker the night, the better,” said Haddock.

Where can I see bioluminescence around the Bay Area?

Haddock says that if the bioluminescence is very bright, you can see it really well on the shore or on the bluffs overlooking the shore.

But one of his best experiences seeing bioluminescence was on a rowboat in a bay.

“Every drip of water from the paddle would create this concentric ring of lights that went out,” he said. “It’s just amazing.”

The two most common spots to check out bioluminescence are Tomales Bay in Marin County and Moss Landing in Monterey Bay where you can take advantage of a number of bioluminescent tours organized by kayaking companies.

In Santa Cruz county, residents have spotted bioluminescence on the shores of Manresa State Beach in Aptos, Seacliff State Beach, Rio Del Mar State Beach, Shark Fin Cove in Davenport, Platforms Beach and Sumner Beach in Aptos. Big Sur near Bixby Bridge has been known to produce bioluminescence in 2018.

For folks who want to experience this event with others, Haddock advises checking out kayaking companies that offer bioluminescence tours. Bay Area kayak companies like Kayak Connection and Blue Waters Kayaking offer bioluminescence tours every year from June until around November.

What’s it like to go on one of these bioluminescence tours via kayak — especially if you’re already a science lover? Bay Area scientist Nuur Shaikh, who majored in biology in college, recently accompanied almost 20 other friends on a bioluminescence tour in Moss Landing, Santa Cruz, where the tour guides brought them to the bioluminescent hot spots in Elkhorn Slough.

“The current was basically pulling us toward the hot spots. We didn’t really have to row or anything,” she said.

On the way to the bioluminescent hot spots, Shaikh and her group passed by patches of algae. “So you could pick up a piece of algae and you can kind of see the [bioluminescent] plankton that’s stuck on those strands,” she said.

When she twirled her fingers in the water, she said the water would light up for a microsecond, making it look like glitter.

“They kind of sparkle a little,” she said. “They look like fairy dust.”

Tell us: What else do you need information about?

At KQED News, we know that it can sometimes be hard to track down the answers to navigate life in the Bay Area in 2023. We’ve published clear, practical explainers and guides about COVID, how to cope with intense winter weather and how to exercise your right to protest safely.

So tell us: What do you need to know more about? Tell us, and you could see your question answered online or on social media. What you submit will make our reporting stronger, and help us decide what to cover here on our site, and on KQED Public Radio, too.