Unexplained, but not an oil spill: A huge school of anchovies gathered off the coast of La Jolla, in California's south, on Tuesday
Or so it appeared.
In truth the ominous dark band that formed off the coast of La Jolla, in the state's south, was a massive school of Northern anchovies.
However the anchovy aggregation has baffled scientists, who say they have not seen anything like it in the area for over 30 years, according to The LA Times.
Scientists say there hasn't been a sighting of a school this big in the area for at least 30 years
Students from the nearby Scripps Institution of Oceanography at UC San Diego decided to get in the water for a closer look
The fish caused a big bland to form in the water, which one onlooker described as like a lava lamp
Video of the sooty shearwaters descending upon Monterey Bay - taken Monday night by hopeful whale watchers - depicts a scene that Grind TV described as 'Hitchockian'.
A humpback whale even appears in one of the videos, which quickly spread on social media.
'It's fun to see nature when it behaves like this,' commented on Facebook user.
Robert Monroe, a communications officer with Scripps Institution of Oceanography at UC San Diego, filmed the school of anchovies and said he initially believed it to be an oil slick.
'It was remarkable,' Monroe told The Los Angeles Times.
'From a distance it looked like an oil slick and you think 'What happened?' and then you get up close and it's amazing.
'It's like watching the motion of a lava lamp.
And now it's dinner: The anchovies have attracted tens of thousands of hungry seabirds
The sooty shearwaters were seen in feeding in Monterey Bay from whale watchers
'This is not an oil slick off Scripps Pier. It's a school of anchovy no one can recall seeing this close to shore in 30 years.'
Phil Hastings, a marine biologist professor and curator of the Scripps Marine Vertebrate Collection, told City News Service the millions of anchovies were first spotted Monday by lifeguards.
All of them were mostly gone by Tuesday evening.
'Leopard sharks [one is seen in the video] were feeding on them this morning,' Hastings told CNS.
Hastings said the water at the pier was 74 degrees and 'pretty much the warmest water the species has been reported in'.
