The hydrographical phenomena are shaped by climate, geological build and the surface features. 99.7% of the territory of Poland lies in the catchment of the Baltic Sea, mainly in the basins of the Vistula and Oder rivers. Very small pieces of the territory of Poland belong to the catchments of the Black and North Seas.

About 90% of the basins of our main rivers – Vistula and Oder lay on the territory of Poland. Their characteristic feature is an asymmetric build – both basins have a better developed eastern side. Low (lowland) watersheds influence the high hydrographical congruity of the territory of Poland.

Similarly to Finland and Sweden, Poland is a country which has got a large number of lakes. On its territory there are over 9,000 lakes, whose surface size exceeds 1 ha. The majority of them are of glacial origin. The largest number of lakes is in the Pomeranian Lake District. Second largest number of lakes is in the Masurian Lake District, but the total surface of these lakes is larger than in the Pomeranian Lake District. Significant agglomerations of lakes occur also in the Wielopolsko-Kujawski Lake District and Polesie Lubelskie.

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