Small amounts of methane detected in the water off Santa Monica on Sunday was the cause of a foul odor, authorities say.
The smell was reported along the coast from Sunset Boulevard to south of Venice Beach.
It may have been caused by a change in the water temperature that could have caused plankton and algae beds to bloom, releasing methane just under the surface, SMFD communications officer Justin Walker told the LA Times.
The amount of methane was too small to be hazardous to health and no illnesses were reported.
Methane readings had dissipated by about noon Sunday.