Marsh is one of the most important and preserved ecosystems. Due to the hilly and woody landscape structure of the Žemaitija National Park, a lot of marshes of different sizes had been formed in the lowlands between the hills.
The typical example of the western Žemaitijos upland bog is the marsh of Šarnelė in the wetland of Paparčiai. The medium-sized low-lying marshy lands of the alkali type prevail in the Park. The marshes of Siberija, Šeirė, Stirbaičiai, Lieptai, Velėnijos, Sidabrinė, Paburgis, Juodupis, Briedinė and others are interesting because of its dense groves of sedge turning into the clearings of the short grass and peat-moss. In the marshes of the Park the botanists found the populations of Sphagnum subnitens, Liparis loeselii, Hammarbya paludosa, Coralorchiza trifida, Listera cordata, Dactylorhiza maculata and of very rare Scolochloa festucacea.
Marshes are very important for biological diversity of birds, animals and mushrooms. There are lots of nests of very rare and endangered birds: crane, curlew, snipe, yellow wagtail and others. Small marshes and ponds formed by beavers are extremely important for the bological diversity during first 5 to 8 years.
These low-lying marshy lands and sedgy quags are protected areas in the EU.