The grasslands that are frequently inundated are one of the most dynamic of the habitats. They cover about 30% of the area of Lonjsko Polje Nature Park. As a result of the periodic dynamics of flooding by the waters of the Sava River and its tributaries, the hay meadows and pasturelands grazed by the livestock of Lonjsko Polje and Mokro Polje are flooded partially or completely for some 30 to 100 days almost every year. They have an important role as a retention area in the flood defence system, and also have a great ecological and economic value as part of the traditional system of pasturing and in the preservation of the landrace breeds. Apart from that, here is one of the most important spawning grounds for carp in the whole of the Danube basin, only in Lonjsko Polje does the spoonbill use the pastureland as a feeding site, and the corncrake nests not only in the hay meadows of Lonjsko Polje but also in the natural meadows of high sedges.