EN
Mires in the largest of the three basins forming the Biebrza Wetlands are dehydrated over most of their area (77%). Different degree of dehydration is indicated by the state of transformation of peat soils and the floristic composition of plant communities. Mire sites transformed as a result of dehydration are also found on the territory of the Biebrza National Park. They require renaturization to regain qualities typical for natural mires. The present article describes the Middle Biebrza Basin distinguishing it into four distinct parts differing in terms of their site conditions. Soils, plant communities, hydrology and effects of dehydration in each of the four parts are outlined together with measures needed to achieve site renaturization. Objectives and trends of renaturization vary depending on which of the distinguished parts of the Basin they concern. Their analysis will assist in defining the scope and order of the elaboration of principles for regulating the water regime in the entire Basin in keeping with the needs of agriculture and protection, including renaturization of sites found inside the Biebrza National Park.