The freshwater marsh in Bertoški bonifika was arranged as a substitute habitat for destroyed wetlands, which have spread out at the mouth of the Badaševica river before 1990. A variety of freshwater habitats, typical for the Adriatic Sea river deltas, allows suitable habitat conditions for a large number of plant and animal species.
The water from Rižana river left discharging channel brings life to the freshwater marsh consisting of wet and marshy meadows, open water areas, reedbed and termophile shrubs, all being full of variety of food. The abundance of freshwater life ranging from the aquatic plants to small aquatic organisms, such as molluscs, crustaceans, larvae of dragonflies and water beetles, frogs, tadpoles and small fish, attract large flocks of waders and herons. Those birds – most of them with long legs and beaks – find plenty of food in the soft marshy ground, ditches and shallows. During migration and wintering, wet meadows and open waters in the freshwater part of the reserve also attract large flocks of ducks, geese and swans, particularly geese (Anser sp.) and various species of ducks (Anas sp.), which mainly feed on plant food: leaves of aquatic plants, buds of grass and reeds as well as roots. Some duck species of the Aythya genus use diving to find their food.