CHELMSFORD (CBS) – Search crews found a body late Monday morning believed to be that of a 16-year-old girl who went missing after a jet ski collision on the Merrimack River.

The teen from Lowell was knocked into the water after police say a man drunkenly hit the jet ski she was riding from behind late Sunday night.

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Chelmsford Police said Douglas Dematos, 32, a friend of the victim, was arrested and charged with boating under the influence, operating a jet ski at night, and more.

He was arraigned in his hospital bed Monday afternoon and ordered held on $7,500 bail.

Douglas Dematos, charged with boating under the influence in a jet ski crash that left a teen missing. (WBZ-TV)

Earlier in the day, officials held a press conference to say they had found the body.

“We have, a short time ago, recovered a body from the river,” Middlesex District Attorney Marian Ryan at a press conference Monday. “We believe that to be the body of the young woman who was on the jet ski.”

Ryan said they wouldn’t be releasing any further identification pending a determination from the medical examiner’s office.

The girl, whose name has not been made public, was riding on the back of her boyfriend’s jet ski on the Merrimack River just before 11 p.m. Sunday when, according to her family, they were hit from behind by another jet ski–which police say was driven by Dematos.

“These individuals were out on the river in watercraft without lights,” said Chelmsford Chief of Police James Spinney. “That’s against the law … these small craft are very very fast. They can be very difficult to control going that fast, and it doesn’t take much to lose that control. And when you couple that with possible inebriation, it’s a combination for a tragedy like this.”

Firefighters said one person was pulled from the water and taken to a hospital, but the 16-year-old was apparently thrown into the water and couldn’t be found.

When police responded to the scene, they said they observed Dematos showing signs of intoxication.

Dematos’ attorney disputes that he was drunk at the time. “He doesn’t remember a lot of what happened,” said attorney Fran Dallmeyer. “Your honor a lot of the signs of intoxication can also be signs of head injury and he suffered a head injury as a result of the accident.”

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Two jet skis were towed from the scene.

The teen’s family watched from the edge of the Merrimack River early Monday as Chelmsford Police launched a search boat. (WBZ-TV)

Rescue boats and a helicopter searched the water for five hours overnight.

Family members could be seen consoling each other as they anxiously awaited word on the shore.

“It’s hard, because we don’t know what happened, if she’s alive or not,” the teen’s cousin, Arthur Campos, told WBZ-TV Monday.

The search, which covers an area of approximately 2 miles, resumed early Monday morning with a dive team joining the effort.

Later on Monday morning, sonar equipment found the body about 14 feet below the water.

“Obviously a very tragic and sad ending to this incident,” said Chief Spinney.

Dematos is currently being treated for non-life-threatening injuries.

A judge ordered him not to drink any alcohol and to submit to random alcohol screenings.

He’s due back in court September 8.

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WBZ NewsRadio 1030’s Bernice Corpuz reports