The Danube rose to its highest level in more than a century on Saturday, but the breaching of a dam in Romania eased pressure on towns and villages struggling to hold back the floods, officials said.
Rivers fed by heavy rain and melting snow crept higher across the Balkans for the fourth straight day, driving people from their homes and swamping low-lying farmland and ports.
Waters rose to an 111-year high in the Romanian town of Bazias, near the Serbian border, flooding around 5,000 hectares of farmland on the Danube's 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 on both sides of the river.
Romania's government started controlled flooding to divert water, flowing near a record 15,800 cubic metres per second, away from low-lying villages and was helped by the collapse of a dam in southwestern Romania which flooded farmland.
"The water flow has fallen by 200 cubic metres per second. This is a success," Beatrice Popescu, of the Environment Ministry, said.
In all, Romania plans to submerge 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 Balkans are 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, leaving thousands homeless and leaving tens of thousands more at risk.
Officials said the Danube's level should remain high until Wednesday and Thursday, but the controlled flooding in Romania appeared to keep its level steady in many places, giving a reprieve to some towns that had been partially submerged.
In the Bulgarian port city of Lom, 120 soldiers came to reinforce civil defence workers, but water levels were unchanged at a record 9.45 metres.
"There is no reason to panic," Bulgarian Prime Minister Sergei Stanishev told reporters. "We are ready to evacuate people if there's a need, but I hope it will not happen."
In Serbia, the floods killed their first victim in the village of Stari Kostolac on Friday where water reached the roofs of 200 houses. The Danube's level dropped in the city of Novi Sad, but authorities braced downstream in Belgrade for a eastern-moving floodwave, which originated in central Europe.
At the village of Mosorin on the Tisa river, 250 people worked to shore up dykes at critical spots. Agriculture Minister Ivana Dulic Markovic said the berms could fail and told officials to prepare for evacuation, Beta news agency reported.
"We are all mobilised and what is left now is for us to trust in God that all will end well," she was quoted as saying.
Hundreds of citizens and soldiers also worked overnight to build an embankment in the eastern town of Smederevo after water inundated its ancient fortress, port and train station.
The Agriculture Ministry said 223,000 hectares of farmland were under water but could not estimate damages until later.
Back in Romania's western county of Timis, the country's worst hit region in last year's floods, some who were displaced last year were again visited by disaster.
"If the government expected floods again this year, why did they move us here?" Ioan Subulescu, whose new house has been partially flooded, told the Evenimentul Zilei paper.
