When will the stink from San Diego County’s red tide go away? Scientists aren’t sure

Algae blooms, also known as red tides, have turned the ocean water brown at La Jolla and along the rest of the San Diego coast. The algae deplete the water of oxygen and often kill fish. This year’s algae bloom has been bigger and lasted longer than in most years.
(K.C. Alfred / The San Diego Union-Tribune)

UCSD researchers say a lack of coastal winds might be allowing the bloom to persist.


Scientists at UC San Diego said Wednesday, May 13, that the red tide along the San Diego County coastline is lasting longer than expected, and they’re not sure when the algae bloom will stop producing a foul smell that’s sometimes noticeable miles inland.

In recent weeks, the naturally occurring phenomenon also has been killing everything from snails and sea cucumbers to calico bass and moray eels.

The red tide is not classified as a major public health hazard. But researchers say it can cause respiratory problems in some people, especially those with emphysema or asthma.

“We didn’t expect this bloom to go on for two months,” said Clarissa Anderson, executive director of UCSD’s Southern California Coastal Ocean Observing System, or SCCOOS. “They’re usually much shorter, and there usually isn’t a mass die-off of fish.

“There are tell-tale signs that this one might be dissipating. But we don’t have a good model to help us determine what will happen.”

The bloom began to arise in late March and SCCOOS researchers quickly noticed that it contained Lingulodinium polyedra, a single-cell organism that can produce brilliant flickers of neon light in the ocean known as bioluminescence.

The lights are only visible in the dark. Even so, many people in San Diego County stopped sheltering-in-place from the novel coronavirus long enough to visit local beaches to see the pretty flashes.

The blue glow lighting up the nighttime surf recently in the Scripps Pier area of La Jolla and other spots along the San Diego County coast is bioluminescence, a natural light show produced by tiny organisms.

That sense of enchantment has faded in recent weeks. Although most algae blooms are beneficial, this one is not. The L.poly organism carries a toxin that can kill fish and birds. The organism also depletes the amount of oxygen in the ocean, further stressing animals.

The algae produces a noxious smell as it dies off. The odor is compounded by the chemical reaction that occurs when bacteria feasts on the algae, researchers say. The sea breeze has been carrying the smell east of Interstate 5 in many parts of the county.

Although scientists aren’t sure why the red tide is lasting so long, Anderson said the lack of seasonal winds along the coast might be a factor.

“We’re not getting the kind of upwelling we normally get this time of year,” Anderson said. “We don’t have a lot of mixing in the water column, the kind that would help break up something like this.”

— Gary Robbins is a reporter for The San Diego Union-Tribune