Long Islanders thought winter had arrived early when they walked near the Shinnecock Canal in Hampton Bays, New York, on Monday.

The water looked like it was covered in a thick sheet of ice, but upon closer examination, residents could see it was actually thousands of silver bunker fish wiggling on top of each other, struggling to survive.

Dozens of people posted pictures and videos of the unusual sight on Facebook.

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“Strange phenomenon. Cause of man or nature?” local resident Gustavo Zuluaga Buritica asked.

“Wow never seen anything like it!” Long Islander Eric Reilly commented.

As videos of the rare sight go viral, people are now looking for answers.

The New York State Department of Environmental Conservation told CBS News on Tuesday that they are monitoring the incident.

“No additional fish kills have been reported overnight or today,” said Erica Ringewald, the department’s media relations director. “Some dead bunker are floating in the Shinnecock Bay but most are believed to have sunk to the bottom.”

The town of Southampton has been cleaning up the dead fish on the beaches and DEC Marine Resources is arranging for aerial overflights to track the movement of the dead fish, Ringewald explained.

“Southampton worked with the County Department of Public Works to open and close the canal to keep the oxygen levels up while allowing some fish to escape,” she said.

While state environmental officials didn’t identify a cause for the massive die-off, local experts have an idea.

“There was a big school of blue fish in the bay earlier on Sunday,” Stony Brook Southampton Marine Science Center manager Chris Paparo told CBS New York. “Blue fish eat bunker and they chase the bunker into the canal like this and the locks are closed, fish can’t escape, and when they get pushed in they deplete the oxygen.”

Posted by Dennis Demarco on Monday, November 14, 2016

Paparo’s theory falls into line with what most internet users believed to be the cause as well.

Dennis Demarco, who lives in Valley Stream, New York, shared a video of the scene, which has since gone viral with nearly 10 million views.

“Unbelievable scene — tons and tons of bunker starving for oxygen,” he can be heard saying in the video. “Even the locals have not seen anything like this before.”