Mistaken for an Oil Spill, this Shadow in the Sea Will Surprise You

Beachgoers in La Jolla, California took in a disturbing sight as they gazed out onto the ocean on July 8th, 2014. A dark, undulating shadow was making its way toward the sand, creating massive blotches in the otherwise crystalline blue-green waters. They feared it was an oil spill, which would take a harsh toll on the local ecosystem and economy. But when experts were called in, they found that the cause was something they never would have guessed.


As ominous as those dark shadows may have looked, their cause was altogether natural and innocent: an enormous aggregation of tiny fish. Anchovies, to be exact. This incident was unusual not just for its sheer size, but because anchovies typically keep their distance from the shore.  

Photo by David Checkeley

Scientists at the Scripps Institution of Oceanography took photos and video of the phenomenon, noting that it’s “unclear why the unusually large school moved into shallow waters off the coast.”

Photo by Phil Hastings

The size of the school is estimated to be anywhere between 1 million and 100 million. It’s possible that changing ocean temperatures caused the anchovy influx along the shore. Whatever the cause, the phenomenon certainly made anchovy-loving California sea lions happy.

Photos reproduced with permission from Scripps Institution of Oceanography, UC San Diego 

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