A 12-year-old boy drowned on an annual middle school trip after he was thrown from a capsized raft in Pennsylvania.

Cesar Albarracin Guncay, a sixth grader at Pierson Middle School in Sag Harbor, New York, died on May 27 while rafting on the Lehigh River in the Poconos, according to the Carbon County Coroner's Office.

He was one of five people aboard an inflatable raft that was part of a larger guided excursion, authorities said.

When the boat overturned, Cesar was the only person to never resurface from the water, which prompted an immediate search and rescue at mile marker 99 of the river.

He was pronounced dead at 6.50pm after being taken back ashore by the Lehighton Fire Department dive team.

Cesar's cousin, Ashley Buestan, said the preteen was from Ecuador and had come to the US about three years ago.

'It's confusing, it's overwhelming,' Buestan told NBC New York.

She said Cesar was looking forward to going rafting and remembered him as loving art and soccer.

Buestan added that her younger sister was also on the trip and watched the tragedy unfold.

'That's her best friend,' she told the outlet. 'It was always the two of them.'

The trip to Whitewater Rafting Adventures in Nesquehoning was made up of 74 students, the East Hampton Star reported.

This was the third year that the sixth grade class had gone to the Poconos.

A since-removed itinerary on the school's website said the middle schoolers would zipline, go swimming and have lunch before going rafting, according to the outlet.

The rafting would happen on an 11-mile section of the river that typically takes four hours to traverse.

Water levels in the Lehigh River were about 3.6 feet when the children began the journey on 13 rafts.

Around the end of their route, they found a fallen tree that was taking up a large part of the river, the outlet reported, citing some of the children's parents.

Pennsylvania Fish and Boat Commission spokesperson Mike Parker said that life jackets were being used when Cesar's drowning took place, according to NBC News.

Parker added that 'fatalities are not something they deal with often' and said the incident would trigger a review of all safety equipment.

'But even with a life jacket on, there's still other factors,' he said. 'Unfortunately, that's what we seem to be dealing with in this case.'

The owners of Whitewater Rafting Adventures, Hilary and Steve Bretzik, told the outlet that their 'entire team is heartbroken by what occurred' and that their first concern was for Cesar's family and friends.

The superintendent of the Sag Harbor School District, Jeff Nichols, said in a statement that Cesar's death 'will leave an irreplaceable space in our classrooms, our hallways and our lives.'

Nichols said school counselors and support staff would be available to students, families and staff.

'Grief can feel overwhelming, especially for young people trying to make sense of something so heartbreaking,' Nichols said.

Students were set to stay overnight but left early after the drowning and got back around 2am Thursday, a Sag Harbor school district spokeswoman told Newsday.

Cesar's autopsy was completed on Thursday at the Lehigh County Coroner's Office and Forensic Center.

His cause and manner of death was determined to be accidental drowning.

A GoFundMe started to support Cesar's family remembered him as a 'a kind, handsome and athletic 6th grader, a friend to many, and a beloved neighborhood kid here in Sag Harbor.'

'He is immediately missed by his classmates, teachers, school families and the entire community,' the memorial read.

As of Saturday evening, about $232,000 of an initial $350,000 goal had been raised.

Sag Harbor Village mayor Thomas Gardella said Friday that the town would lower its flags to half-mast after Cesar's death.

The Daily Mail has reached out to Cesar’s family, the Sag Harbor Union Free School District, the Pennsylvania Fish and Boat Commission and Whitewater Rafting Adventures for further comment.