The Sinar Bangun tourist ferry had a maximum capacity of 60.
But as the sun began to set on Monday evening, more than 200 people are thought to have crammed aboard the small, rickety vessel to make the 40-minute journey across Lake Toba, on the Indonesian province of North Sumatra.
Many of those on board were young families returning home to celebrate Eid al-Fitr, the Muslim holiday that marks the end of the holy month of Ramadan, which this year lasts until June 21.
Within 20 minutes most of those passengers would be dead, trapped inside the vessel's main cabin as it overturned and sank.
Moments before the accident high waves of up to three meters are thought to have buffeted the boat, rocking it from side to side.
"When the boat started to list I jumped into the water and swam as far away as I could," said Rudi Wibowo, one of only 18 people to have been pulled from the water alive, all within a few hours of the sinking.
Wibowo had been on the island of Samosir in the middle of Lake Toba as part of a camping trip with nine friends. He saw all of them drown.
The majority of those who survived were outside on the front deck, as they had arrived late and the seating areas were full, Wibowo told CNN, who trod water for an hour before he was rescued.
"The passengers inside were unable to break the windows and escape," said Wibowo.
