Located on the Oder River, the anti-flood reservoir was built following lesson from the 1997 “flood of the century” that devastated the two cities. It took a decade and some 2 billion zlotys ($520 million) to build and two villages had to be resettled. Part of the funds came from the European Union and the World Bank. https://apnews.com/article/poland-flood-wroclaw-oder-reservoir-b047703afff41a8b5747ad5efa793c6b