The mother of Uber’s top executive has been killed in a boating accident in California in what the company described as an “unspeakable tragedy” on Saturday. CEO Travis Kalanick’s mother, Bonnie Kalanick, was in a boat with Kalanick’s father, Donald, when authorities say it hit a rock and sank on Friday afternoon. The two were found on the shore of Pine Flat Lake in Fresno County, and Kalanick’s mother was reportedly dead when rescuers arrived. It was not immediately clear if she drowned or died from injuries caused by the collision. Kalanick’s father was hospitalized with moderate injuries. After initially being listed in serious condition, he had reportedly stabilized by Saturday afternoon. While Kalanick has not yet issued a statement on the tragedy, Uber offered its condolences in a statement on Saturday. “Our thoughts and prayers are with Travis and his family in this heartbreaking time,” the ride-hailing service said. Authorities in Fresno say an investigation into the incident is underway, with an autopsy planned for Sunday.