Śniardwy is a lake in the Masurian Lake District of the Warmian-Masurian Voivodeship, Poland. At 113.8 square kilometres, Śniardwy is the largest lake in Poland. It was also the largest lake in Prussia and in Germany, when Warmia-Masuria was under German rule and formed the southern part of East Prussia. It is 22.1 kilometres long and 13.4 kilometres wi…Śniardwy is a lake in the Masurian Lake District of the Warmian-Masurian Voivodeship, Poland. At 113.8 square kilometres, Śniardwy is the largest lake in Poland. It was also the largest lake in Prussia and in Germany, when Warmia-Masuria was under German rule and formed the southern part of East Prussia. It is 22.1 kilometres long and 13.4 kilometres wide. The maximum depth is 23 metres. There are eight islands on the Śniardwy lake.