Międzyodrze is a giant river island limited by western and eastern (Regalica) branches of the Oder river. Its major part, the Landscape Park of the Lower Oder Valley, is protected. All its area is crisscrossed by a thick net of old river beds, small bodies of water, channels and ditches. It is the largest active European peatland with vegetation which has already disappeared in other estuaries. There is no permanent human settlement in this vast area. The author summarizes field studies aimed at defining the threats to this ecosystem.