The cleanest, clearest, deepest (the depth is 48,5 m) and the largest lake ( the area is 1205 ha) in Žemaitija - Plateliai Lake. There are seven islands in the lake: Briedsalė, Pliksalė, Ubagsalė, Gaidsalė, Veršių, Pilies and Šončelio. Natural heritage sites are the all 7 islands and 2 peninsulas. Complicated processes of glacial and post - glacial periods formed hilly, ridged confirmation, blocks of ice scraped deep waterholes of lakes, drifts of melding ice subsided in rifts forming the cobweb of shoals, islands and peninsulas. Till hills surround deep valleys of lakes and marsh. The highest hills are in the eastern part of the lake - in the forest of Plokščiai.

Both on higher hills and in deep hollows there are dense shady fir- groves. They are peculiar valuables of our Park. Natural old coniferous woods, fir- trees mixed with pine- tree and very little birches and asps are called Western taiga following the classification of biotops of the European Union. That`s why they are preserved and treasured in Europe. Fir - groves occupy the biggest part of the Park (47%).

On the eastern coast of Plateliai lake and in the peninsulas of Kreiviškiai and Auksalė there are fragments of old pines left. Birds in danger, such as goshawks, eagles, kites build their nests in the crowns. They are only small spots of decidious woods left. You can find them in the wood of Liepija, in the some parts of the wood of Stirbaičiai, in the islands of Pliksalė and Pilies and in the peninsula of Kreiviškiai. Lots of creatures hide in the hollows of trees: birds, bats, mice, dormice, martens. In springy hollows there are old groves of black alder, soaked birch groves and other swamp woods which are very interesting. Thanks to mosaic, hilly conformation of Žemaitija National Park there are lots of swamps.

Alkaline fens - type swamps of Siberija, Šeirė, Lieptų, Velėnijų and others are rich with rare plants. Here the bigger part of preserved orchid - type plants and lots of moss inscribed into the Red book of Lithuania were found.