The 33-year-old had been boating with her son on Lake Piru, the Ventura County Sheriff’s Department said. Rivera rented a boat around 1 p.m., the department reported, and her son was found napping alone in the vessel three hours later. Rivera’s son said the pair had been swimming, but Rivera never returned, according to Capt. Eric Buschow. The boy was wearing a life vest and another adult life vest was found on the boat, he said.