Story highlights An environmental group raises concerns over toxic waste reservoir by Danube 
 
 Budapest's mayor says its flood defenses should withstand record high waters 
 
 The swollen River Elbe continues to threaten Saxony-Anhalt in eastern Germany 
 
 Focus in the Czech Republic shifts to the clean-up operation, fire service says 
 
 Hungary has been warned it could suffer its worst floods ever, as record levels are expected over the next three days from the surging River Danube, which has already inundated parts of Germany, Austria and Slovakia. 
 
 Read more: Swollen rivers bring more flooding in central Europe 
 
 The river is expected to peak near the border with Slovakia, in Nagybajcs, on Saturday morning and in the capital, Budapest, on Monday, according to the European Commission's emergency response center. 
 
 "In both areas, the highest-ever-measured water levels are expected," it said. 
 
 Hungary's Water Management Authority said a new record, 20 centimeters (nearly 8 inches) more than the previous high, had already been set at Nagybajcs as of midday Friday. 
 
 New all-time highs have also been recorded downriver at Komarom, it said. 
 
 The mayor of Budapest, Istvan Tarlos, said he expects a record of 895 centimeters (almost 30 feet) in the capital but he believes its flood defenses should keep the city safe with about a foot to spare. 
 
 Nearly 400 people have been evacuated so far, from a number of villages and an old people's home, according to the Interior Ministry's disaster management directorate. About 70 communities have been hit by flooding. 
 
 The country's military is working on dams along the river's length and is preparing to deploy helicopters and amphibious vehicles if needed. 
 
 One village, Kisoroszi, is already unreachable by road -- although food and help can be brought in by boat and helicopter -- and is expected to remain cut off for at least a week, authorities said. 
 
 Roland Farkas, a Hungarian university student, is among the volunteers who've been filling sandbags day and night in the town of Gyor, near the Danube, to be deployed at vulnerable points. 
 
 He told CNN iReport Friday he feared the country's defenses would fail to hold back the floods in the face of forecast storms. 
 
 Concern is also growing that the surging Danube might break into a reservoir containing toxic waste in Almasfuzito, near Komarom, potentially leading to water pollution. 
 
 Environmental campaign group Greenpeace said in a statement that although the dams should in theory withstand the rising water, a report published by the Hungarian Academy of Science last year suggested some toxic sludge could be washed into the water system through the ground water. 
 
 The reservoir is being closely monitored but the government remains anxious about its safety, the statement said, citing comments by Hungary's prime minister. 
 
 Evacuations along the Elbe 
 
 Meanwhile, the swollen Elbe River menaces the state of Saxony-Anhalt in eastern Germany, where thousands of people are being evacuated from their homes a day after the flow peaked in Dresden, in Saxony. 
 
 Flood defenses saved the center of the historic city from serious damage. 
 
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 But aerial footage taken by CNN showed swaths of the outlying areas and beyond under feet of muddy brown water. Industrial containers are among the debris swept up by the torrent, prompting further concerns over safety. 
 
 The cost of damage to homes, businesses and agriculture is likely to run to hundreds of millions of euros. German Chancellor Angela Merkel promised 100 million euros ($132 million) in emergency aid Tuesday. 
 
 The water is still rising in the Elbe as it makes its way toward the North Sea, according to the European Commission, and it is expected to peak in Saxony-Anhalt on Tuesday. 
 
 Residents are being evacuated from the cities of Halle and Bitterfeld in the state. 
 
 In the state of Saxony, to the south, many areas remain under water, the European Commission said, and transport, electricity and water supply are still disrupted. 
 
 As of Friday, about 12,000 people had been evacuated from their homes in Saxony, it said. 
 
 The cresting Danube, which flooded parts of Bavaria in southern Germany and Austria earlier this week, passed through Slovakia's capital, Bratislava, Thursday without causing significant damage, according to the European Commission. 
 
 An extreme flood alert is still in effect in the western part of Slovakia, including Bratislava, it said. 
 
 Water levels in the Danube and its tributaries in Bavaria are now falling except in the area around Passau, a town that experienced the worst flooding in five centuries this week. 
 
 The flooding has caused at least 15 deaths across the region since last weekend. 
 
 Eight deaths were reported in the Czech Republic, where some 700 communities have been affected by flooding and about 20,000 people evacuated. 
 
 As river levels drop, attention is now turning to the clean-up, said Czech fire service spokeswoman Nicole Zaoralova. 
 
 "The main focus is on draining flooded areas," she said. All the country's large-volume pumps are in use, so offers of help with equipment and manpower from Poland and Slovakia will be taken up, she said. 
 
 Army units have also been deployed to help with the clean-up, she said, with almost 300 troops sent to the affected areas. 
 
 Three deaths occurred Saturday in southwestern Germany, the Interior Ministry for the state of Baden-Wuerttemberg said. Four people are reported to have died and three are missing in Austria, the European Commission's emergency response center said. 
 
 The floods follow heavy rain in the region last weekend, after a wet spring left the ground saturated. 
 
 Scattered showers are likely over the coming day, according to CNN meteorologist Karen Maginnis. 
 
 Read: Floods bring misery to central Europe ||||| Media caption At least 15 people have already been killed in floods across central Europe 
 
 Hungarians have been warned to prepare for their country's worst floods ever as the Danube is set to reach record levels this weekend. 
 
 "We are facing the worst floods of all time," said PM Viktor Orban. 
 
 Europe's second-longest river is set to hit unprecedented levels in the capital Budapest in the next few days. 
 
 A state of emergency has been declared, and thousands of volunteers have been working to reinforce the banks of the swelling river. 
 
 Water levels are set to reach 8.85m (29ft), some 25cm (10in) higher than the Danube's previous record high in 2006. 
 
 Emergency workers have set up camps along the river as residents packed sandbags around their homes amid an atmosphere of concerned expectation, says the BBC's Nick Thorpe in Budapest. 
 
 Kristalina Georgieva, the EU Commissioner for International Co-operation, Humanitarian Aid and Crisis Response, tweeted: "Hungary well prepared for highest ever measured water levels on Danube. We are monitoring & ready to assist." 
 
 Mr Orban, who spent the night at a military barracks in the flooded western city of Gyor, said recent dry weather in Austria and Germany, as well as a hot forecast for Hungary over the weekend, gave reason to hope that Europe's worst river floods for more than a decade could soon be over. 
 
 "The fact is that along the border (where the Danube lies between Hungary and Slovakia) the water level is already above the highest level ever measured," he added. 
 
 Budapest Mayor Istvan Tarlos said that in a worst-case scenario up to 55,000 people may need to be evacuated. 
 
 However, he said he was confident that only the lowest-lying areas would be exposed to the river's expanded flow. 
 
 Nine hundred people have already had to evacuate their homes upstream, the Associated Press news agency reports. 
 
 Mass evacuations 
 
 Widespread flooding in central Europe has inundated swathes of Austria, Germany, Slovakia and the Czech Republic, killing at least 15 people. 
 
 In the Slovak capital Bratislava, the main flood defences held firm against the swelling Danube on Thursday. 
 
 But while river water levels were receding in some areas, the Danube had yet to reach its peak in Slovakia, said the European Commission's newly inaugurated Emergency Response Centre (ERC). 
 
 In northern Germany, workers piled sandbags along the banks of the River Elbe as waters rose, after widespread flooding further south. 
 
 As flood waters receded to the south and east, defence work continued apace near Lueneburg in Lower Saxony. 
 
 Tens of thousands of people have been evacuated from threatened areas in Germany, where the flooding is worse than that recorded in 2002. 
 
 The economic impact might be worse than the 11 billion-euro losses caused by the 2002 floods, said Eric Schweitzer, the president of the German chamber of trade and industry, 
 
 "In some regions, the extent of damage is likely to be rather larger than in 2002," wrote Mr Schweitzer in an editorial for the Rheinische Post newspaper. 
 
 On Thursday the Elbe flooded parts of Dresden as it peaked nearly 7m (22ft) above its normal level, but the city's historic centre remained unscathed. 
 
 Upstream along the Elbe in the Czech Republic, emergency workers used boats to shuttle supplies to stranded people as large areas remained under water.
– Hungary is in need of an ark. As the Danube swells, record-high levels of 29 feet are expected, with waters peaking near the Slovakian border tomorrow and in Budapest on Monday. PM Viktor Orban isn't mincing words: He says the nation could see "the worst floods of all time." With a state of emergency declared, the BBC reports volunteers numbering in the thousands worked through the night to build up the banks of Europe's second-longest river, while 400 people have already been evacuated, according to CNN. That follows the evacuation of tens of thousands in Germany and some 20,000 in the Czech Republic, which, along with Austria, have seen deadly floods that have thus far killed 15.