On the Polish side of the “Oderbruch” the river has no dike and every time the flood flows over an enormous swamp. An ideal environment for mosquitos - which of course makes it ideal for frogs too, and for miles on end one can hear them buzzing in their millions. During the day herds of cows cross the swamp howling for their calves whilst in the trees hundreds of starlings twitter.
Listen to an audio excerpt (MP3, external link).