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MIAMI (CBSMiami) – A man remains missing Monday night after falling off a personal watercraft in the Blue Lagoon.

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“It’s almost like he hit something.  I’m not sure,” said Rick Rojo, who says he witnessed what happened.  “The Jet Ski almost came to a full stop and it just catapulted over, landed head first, feet in the air.”

Chopper4 was over the scene in the area of the Dolphin Expressway East of 57th Avenue around 5 p.m.

A rescue dive team could be seen in a raft on the water as an ambulance was parked near the shore.

“We did find the watercraft that was floating,” said City of Miami Fire Rescue Capt. Ignatius Carroll.  “We did also locate a life vest that was also found in the water.  It has not been determined whether or not it belongs to him or not.”

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Fire officials say the marine patrol units brought out special sonar equipment to assist in the search.

“The area that we’re going to be searching varies in depth,” said Carroll.  “But you can imagine with the lagoon you got water that is very murky.  You got a lot of seaweed that is out there.   So it’s not going to be an easy search to undertake.”

Crews say they searched for about an hour and a half, finding no sign of the man.

“This rescue effort has now turned into a recovery effort,” said Carroll.

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Authorities have not released the man’s name.  They say it’s unknown whether the man owned the personal watercraft or how much experience he had operating it.