Waters rose to a 111 year high in the Romanian town of Bazias, near its border with Serbia, flooding around 5,000 hectares of farmland on the northern bank.
The river also flooded the small port of Bechet, while soldiers and civil defence workers scrambled to reinforce dykes and build sandbag barriers.
Romania's government have started controlled flooding to divert water, flowing near a record 15,800 cubic metres a second, away from low-lying villages.
They have been helped by the collapse of a dam in south-western Romania which flooded farmland.
Romania plans to submerge, in all, about 90,000 hectares of fertile soil on a 400 kilometre stretch on the Danube's northern bank, a major area for wheat and maize farming.
The region is still recovering from devastating floods last summer, which killed scores of people and caused hundreds of
millions of euros in damage to farmland and infrastructure.
This time, floods have submerged hundreds of houses across the Balkans, displacing thousands of people and leaving tens of thousands more at risk.