WARSAW, Poland — A frightened, shivering dog was rescued after floating at least 75 miles on an ice floe down Poland’s Vistula River and into the Baltic Sea, officials said Thursday. Now his saviors have to figure out who owns him. Rescuers have named the miracle dog Baltic. The dog’s odyssey came as Poland suffers through a winter cold snap, with temperatures dipping to below minus 4 degrees Fahrenheit. The thick-furred male dog was found adrift Monday 15 miles out in the Baltic Sea by the crew of the Baltica, a Polish ship of ocean scientists carrying out research. A firefighter in Grudziadz, on the Vistula River, said the dog was spotted Saturday floating through the city. The dog didn’t welcome three would-be owners on Wednesday and Thursday. Two others were coming to Gdynia for a possible reunion.