Canada's Transportation Safety Board thinks it knows how a whale-watching boat sank on Sunday, leaving five Brits dead and an Australian missing: a surprise wave, the Guardian reports. A survivor told one of the rescuers there was "this real big wave coming—bigger than the rest of the big rollers ... it picked the boat off and it fell off the wave, it started tumbling," per the Globe and Mail. Although the weather was said to have been calm, local sailors say strong currents and rogue waves can happen even then, the BBC notes. And although the vessel's owner says it was manned by a veteran skipper and had safely made the same trip every day for 20 years, the boat's design is being scrutinized. "We know that most passengers were on the top deck on the port side," an investigator with the board tells the Guardian. "This would have raised the center of gravity, affecting the vessel's stability."
Details are now trickling out about the victims—all of whom had been standing on the top deck and none of whom had life jackets on, the British Columbia coroner notes—including an 18-year-old with Down syndrome and his 50-year-old father, per the Guardian. Meanwhile, local fishermen from a Native American tribe who were among the first to the site after seeing a flare go up are being praised for their efforts. "More lives would have been lost if not for the [Ahousaht] First Nation," BC Premier Christy Clark tells the paper. "We're all incredibly grateful." Those who helped recall people clinging to the boat (which the BBC notes had no time to send out a mayday signal) and covered in diesel fuel. "It's something you really can't describe," one rescuer tells the Guardian. "It's going to be held with me for the rest of my life." (A tourist was killed by a jumping whale in Mexico.)