A small ferry ship makes its way among ice-floes floating in River Danube north of Budapest, Hungary on Monday.
Authorities say up to 90 percent of the river surface is covered with floating ice, making it extremely difficult to traverse Europe's main commercial waterway, which winds 1,777 miles (2,860 kilometers) from Germany through Austria and Hungary and serves as the natural border between Bulgaria and Romania as it flows out to the Black Sea.
Deadly floods follow in iced-over Europe
Romania and Bulgaria's decision come the day after Serbian emergency officials said the country's army will use explosives to break up ice on the Danube and Ibar rivers to try to prevent the possibility of flooding.


