1. Fish
1.1. Trout
1.1.1. The common name for a number of species of freshwater fish belonging to the genera Oncorhynchus, Salmo and Salvelinus, all of the subfamily Salmoninae of the family Salmonidae.
1.2. Salmon
1.2.1. The common name for several species of ray-finned fish in the family Salmonidae. Salmon are native to tributaries of the North Atlantic (genus Salmo) and Pacific Ocean (genus Oncorhynchus).
1.3. Sander
1.3.1. A genus of fish in the Percidae (perch) family. They are also known as "pike-perch".
1.4. Catfish
1.4.1. A diverse group of ray-finned fish. Named for their prominent barbels, which resemble a cat's whiskers, catfish range in size and behavior from the three largest species.
1.5. Eel
1.5.1. Any fish belonging to the order Anguilliformes. Most eels are predators.
2. Other water animals
2.1. Beaver
2.1.1. Beavers are known for building dams, canals, and lodges (homes). Beavers live in Wigry National Park http://www.wigry.org.pl/bobry/hist_en.htm
2.2. Duck
2.2.1. Mostly smaller than the swans and geese, and may be found in both fresh water and sea water.