The water had been building since 5 July, when record rainfall pushed the Oder above its previous high-water mark at Racibórz-Miedonia by more than two metres. Wrocław sits on the river's broad lower plain, threaded with islands and historic bridges, and on the morning of 12 July a single flood pulse from the Oder met another from the Widawa just upstream of the old town. The combined wave overtopped earthworks that had stood for generations. Power failed across hospitals, vaccines ran out, and a cemetery and a landfill were both submerged in the first days, raising real fears of epidemic. Residents tuned to Lower Silesian Television and local radio learned, over the static, how to signal helicopters from rooftops: a white sheet for general help, red for medical.

Estimates from the City Office put the number of sandbags laid in Wrocław between 300,000 and 480,000. There was no system in place to move that much material that fast, so the city improvised. Sand stockpiled for street repairs was scooped up by the truckload, including a long sub-base on General Józef Haller Street that had been carefully prepared and was now simply dug back up. Children's sandboxes across the city were emptied. Soil came from lawns. Bags arrived by air from as far as Gdańsk. In the most threatened districts, especially in the early hours, the lines on the dykes were almost entirely volunteers who had walked in from the surrounding neighbourhoods carrying whatever shovels they had at home. Older residents fought to save sentimental belongings and modest apartments. Younger ones treated the river as something to be beaten, swimming through flooded streets and, in one widely circulated story, diving into a submerged liquor store.

Not every decision could be made by consensus. On the night of 11 July, sappers arrived at the village of Łany, just upriver from Wrocław, with explosives prepared to breach the embankment and bleed pressure off the wave before it reached the city. Residents of Łany and neighbouring Kamieniec Wrocławski, alerted by a local, gathered at the dyke and physically blocked the operation. By morning the deputy voivode called it off, citing a 'mistake'. The standoff has been argued about ever since by hydrologists, ethicists and the Supreme Audit Office. The villagers saved their own homes; the additional water that did not bleed off at Łany helped fill Wrocław's downtown. There is no clean moral here, only a small village asked, at midnight, to drown itself for a city it could not see.

By 16 July the water in downtown began to recede and bus services slowly resumed. Cathedral Island, Sand Island, the market square, Wrocław Główny railway station and the Ossolineum library all came through. The philharmonic flooded, but the staff and volunteers rolled the pianos up onto stages and saved them. The Polish Theatre and the Academy of Music's ground floor were not so lucky. In total the flood damaged or inundated 2,583 residential buildings; the city would spend 132 million złoty repairing forty-four kilometres of road and twenty-one bridges and viaducts, with help from the European Bank for Reconstruction and Development, the World Bank, and the EU's Phare program. The 2022 Netflix series Wielka woda, directed by Jan Holoubek and Bartłomiej Ignaciuk, dramatised the days as the wave approached, but the documentary footage from that July is more affecting: ordinary people, many in shorts and t-shirts, passing sandbags hand to hand along a dyke they were not trained to defend, in front of a city they refused to give up.