The Refuge covers the distance (approximately 260 kilometres) of the Bug river, from Krzna eastuary to Zegrzyńskie Lake. Vast majority of the valley was developed into dry, extensively used grasslands.
The swamps are mainly located in the areas of eastuaries of the rivers, Bug tributaries and around former stream beds. The stream bed of Bug is predominantly unchanged by human interference, there are numerous sandy islands – plantless or covered by riparian forests consisting of willows and poplars, with particularly well-developed willos brushwoods. In the first fluvial terrace, there are numerous oxbow lakes, which vary in terms of size, depth and amount of water plants. The Refuge includes also deciduous forests between Drażniew and Platerów.
The forests cover around 20% of the area of the Refuge, whereas the majority are non-forest forms: meadows, grasslands and fields. Natural valley of the big river. Well-preserved natural forests and numerous meadows, associated with relatively wet sites, typically formed on large spaces are particularly precious. Sixteen types of habitats from that area are included in the attachment to the First Directive of the Council 92/43/EWG. 20 species from the second attachment to the Directive of the Council 92/43/EWG were reported to exist there. It is one of the most important areas to preserve different species of fishes in Poland. It includes 10 species of fishes mentioned in the second attachment to the Directive of the Council 92/43/EWG, for example Sabanejewia aurata and white-finned gudgeon. There exist also rare species of plants, including two species mentioned in the second attachment to the Directive of the Council 92/43/EWG. In addition, one can also find a great variety of invertebrates, for example interesting types of spiders. The area is also very important for protecting different bird species.