JAKARTA, Indonesia—Rescue workers deployed a remotely operated vehicle and divers in the deep waters of the world’s largest volcanic lake Wednesday, uncertain how many passengers may have been trapped in a ferry that sank during one of Indonesia’s busiest holiday periods.
Officials said at least four people died and 18 survived when the small vessel overturned Monday night on Lake Toba, on its way from the island of Samosir to the mainland. They believe that many more were on board when it went down in high winds and roughly...