Lower Bug Valley is an area of over sixty thousand hectares, located in Mazowieckie Voivodship, mainly in the region of Ostrołęka and Siedlce. It covers the area along the river Bug, from Krzna river eastuary until the Zegrzyńskie Lake.
Despite the fact, that majority of the valley are agricultural sites (mainly dry grasslands), there are numerous places of high environmental value. Those places include swamps near eastuaries of Bug tributaries or Bug’s former stream beds, which are represented by numerous oxbow lakes (particularly precious due to its diversity and water flora). 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. The riverbanks are covered by willow brushwoods. There are also coniferous and deciduous forests, for example between Drażniew and Platerów. In the Lower Bug Valley one can find species which are very rare in Poland – eastern pasqueflower and marsh angelica (protected by the Directive). The diversity of bird species can be seen in the fact, that there are 39 species of birds (e.g. little grebe, tufted duck, Eurasian coot, tawny owl or western yellow wagtail), protected by the Directive concerning birds. During the breeding period, orntologists may find representatives of Polish Red Book, e.g. short-toed snake eagle, which particularly favours the Lower Bug Valley (it is one of the very few places in Poland where it can be spotted). While looking for birds, one may also find mammals protected by the Directive: European beaver and otter. It is also worthwhile to look for different amphibians and reptiles. In Lower Bug Valley one can spot European fire-bellied toad and pond turtles, which are protected by Natura 2000 network. In the lakes, there are seven species of fishes, protected by the Directive.