Wait for real darkness
Give your eyes 15 to 20 minutes to adjust and stay off your phone screen. The glow is far dimmer in person than in long-exposure photos.
San Diego Red Tide & Bioluminescence Tracker
How to check current conditions, where the glow shows up, and whether the water is safe.
Last updated
Quick answer
A red tide in San Diego is a dense algae bloom — most often the dinoflagellate Lingulodinium polyedra — that turns the water rust-brown by day and can make the surf glow electric blue at night when the waves break. Blooms are unpredictable but most common from late winter through early fall, with major events in spring. To check whether one is happening right now, look at the Scripps Institution of Oceanography coastal observing reports, the San Diego County beach and bay water quality advisory page at sdbeachinfo.com, and recent nighttime surf photos tagged from Torrey Pines, La Jolla Shores, Scripps Pier, Del Mar, Moonlight Beach, and Blacks Beach. The glow appears only in full darkness, is strongest one to three hours after sunset on a moonless night, and shows up where waves break hardest. This particular species does not produce a toxin dangerous to humans, but decaying blooms can irritate eyes, skin, and airways and can trigger low-oxygen fish die-offs — county advisories are the deciding source on whether to enter the water.
Red tide quick reference
| Question | Short answer | Where to verify |
|---|---|---|
| Is it happening now? | Check daily | Scripps coastal observations; local surf reports |
| Is the water safe? | Usually yes, but check advisories | sdbeachinfo.com county advisories |
| Best viewing time | 1-3 hrs after sunset, no moon | Moon phase calendar |
| Best spots | Torrey Pines, La Jolla Shores, Blacks, Del Mar, Moonlight | Scout at dusk |
| How long do blooms last? | Days to several weeks | Varies by event |
| Common season | Late winter through early fall; spring peaks | Historical pattern only |
How to see the glow
Pick a moonless night
A bright moon washes out the effect entirely. New moon nights during an active bloom are the payoff window.
Find breaking waves
The organisms light up under agitation, so a beach with punchy shorebreak beats a calm cove. Kicking wet sand at the waterline also sparks.
Avoid light pollution
Torrey Pines State Beach, Blacks, and the north end of Del Mar are darker than the boardwalk beaches in PB and Mission Beach.
Go safely
Bring a red-filter headlamp, go with someone, watch the tide so you don't get cut off against a bluff, and don't swim at night in unknown surf.
Photograph it right
Tripod, wide fast lens, ISO 1600 to 6400, 2 to 8 seconds. Focus manually on a distant light before it gets dark.
Is the water safe during a red tide?
The common local bloom isn't acutely toxic to people
Lingulodinium polyedra doesn't produce the neurotoxin found in some Gulf Coast red tides, and swimming during a bloom is generally not prohibited.
Decay is the problem
As a bloom collapses it consumes oxygen and produces a strong sulfur smell. That's when respiratory and skin irritation reports spike.
Other blooms behave differently
Domoic acid events from Pseudo-nitzschia affect shellfish and marine mammals. Never harvest shellfish without checking the state advisory.
Check the county before you swim
sdbeachinfo.com posts closures and advisories, including rain-related bacteria warnings that are far more common than algae closures.
Skip it if you're sensitive
People with asthma, young children, and anyone with open wounds should stay out of a visibly discolored or foul-smelling bloom.
Rinse afterward
A freshwater rinse and a wetsuit wash cut down on the itch some swimmers report after time in a dense bloom.
What causes it and why it varies
Upwelling and nutrients
Spring upwelling pushes cold, nutrient-rich water toward the coast, feeding the dinoflagellates that drive local blooms.
Warm, calm surface water
Stratified, still conditions let the organisms concentrate near the surface, which is when the brown daytime color appears.
Runoff after rain
Storm runoff adds nutrients. It also brings bacteria — the 72-hour post-rain swim advisory is separate from and more restrictive than algae guidance.
Why it's unpredictable
Scientists can track a bloom in progress but cannot reliably forecast one. Plan opportunistically rather than booking a trip around it.
The famous 2020 bloom
San Diego's most widely photographed event lasted weeks and drew nightly crowds. Most blooms are shorter and patchier than that one.
How to use this page
- • This is a planning reference, not a live emergency feed. During an active incident, follow instructions from CAL FIRE, San Diego County Emergency Services, and your local fire department.
- • Register for AlertSanDiego and add SD Emergency to your phone before you need them — signing up mid-evacuation is too late.
- • Conditions, schedules, and closures change every year. Confirm event times and beach status with official sources the week of.
- • Nothing here is legal, medical, or insurance advice. When in doubt about water quality or air quality, stay out and stay in.
Frequently asked
Is there a red tide in San Diego right now?
Check the Scripps Institution of Oceanography coastal observations and the county's beach advisory page at sdbeachinfo.com, then look at recent nighttime surf photos from Torrey Pines and La Jolla for confirmation.
Where is the best place to see bioluminescent waves?
Torrey Pines State Beach, Blacks Beach, La Jolla Shores, Del Mar, and Moonlight Beach in Encinitas — all dark enough to see the glow, with waves that break hard enough to trigger it.
What time of night is best?
One to three hours after sunset on a moonless night, once your eyes have fully adjusted. The glow fades in moonlight or near boardwalk lighting.
Is it safe to swim during a red tide?
Generally yes for the common San Diego bloom, which isn't acutely toxic to humans, but decaying blooms can irritate skin, eyes, and airways. Always check county advisories first and skip it if you're asthmatic.
How long does a red tide last?
Anywhere from a few days to several weeks. Blooms move along the coast, so one beach can glow while another a few miles away shows nothing.
What time of year does it happen?
Most often late winter through early fall, with spring the historically most likely window. There's no reliable forecast — it's opportunistic.
Can I eat shellfish during a bloom?
Don't harvest recreational shellfish without checking the California Department of Public Health biotoxin advisory. Commercial shellfish are tested separately and remain safe.
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