"We're presuming that an accident happened and we're presuming she drowned in the lake," Ventura County Sheriffs Deputy Chris Dyer said at a news conference Thursday afternoon. His comments came hours after sheriffs turned the rescue operation for the 33-year-old former Glee star into a recovery operation. Rivera disappeared Wednesday afternoon while boating with her 4-year-old son at Ventura County's Lake Piru. "The goal is still to bring Miss Rivera home to her family," Dyer said. The sheriffs department also released a 911 call after her son was found alone on the boat. UPDATE: Security camera footage of Rivera departing by boat was released.