A trio of good Samaritans dived into a huge pond and rescued a woman after she accidentally reversed her sports utility vehicle into the water. Police said the 68-year-old had pressed the accelerator instead of the brake causing the vehicle to shoot into Spy Pond, a large and deep body of water in Arlington, Massachusetts.

As the vehicle slowly started to sink, onlookers looked on horrified as a man swam into the water and tried, unsuccessfully, to rescue her.

Riding past on their bikes were Dan Frazier and his friend Ken Chapman who had been visiting from Australia. On seeing the distressing scene, they immediately dived into the water and started to help.

"She was very, very scared," Frazier told the WBCV TV station after the 15 October incident. "She knew she was dying. She just figured, 'This is it.' I saw it in her eyes."

As they struggled to get into the vehicle, the first man into the water could be heard screaming: "You've got to come out! You've got to come out," as the vehicle sank beneath the water.

"I lost her. I lost her," he cried.

Frazier said as everyone feared the worst, the woman resurfaced and he was able to help her to the shore, adding that she was "conscious and alert" when she finally made it to dry land.

"I just held her hand and prayed," Frazier said.

She was taken to a local hospital to be treated for mild hypothermia, Arlington Police said in a statement, adding that she was expected to be released on 15 October.

"We commend these citizens for their quick thinking and bravery that ultimately saved this woman's life," they said on Twitter.

The vehicle was completely submerged in the water and police said they would try and remove it once a dive team had checked to make sure the vehicle was unoccupied.