Tree felled by Eurasian beaver (Castor fiber) by Narew River close to Strekowa Gora village, Biebrza National Park, Poland, Europe

Marsh marigolds (kingcups) (Caltha palustris) flowering on flooded Narew sedge marshes, Krzewo, Podlaskie, Poland, Europe

Traditional fishermen's punts chained to a tree beside flooded Narew marshes with flowering marsh marigolds, Krzewo, Poland, Europe

White willow (Salix alba) tree with base of trunk almost chewed through by Eurasian beaver (Castor fiber), Narew marshes, Podlaskie, Poland. MORE INFO: Beaver activity is crucial in keeping Poland's ancient marshes open and free of encroaching bushes and trees and their dams also help to maintain high water levels.

Farmer ploughing at edge of Narew marsh among carpet of Dandelions (Taraxacum sp.) in spring, Podlaskie, Poland.

Eurasian beaver (Castor fiber) dam on drainage channel in Narew marshes, Podlaskie, Poland. MORE INFO: Beaver activity benefits much other wetland wildlife by helping to maintain high water levels in Poland's ancient marshes and swamp forests.

White stork (Ciconia ciconia) adult collecting nest material on Narew marshes in spring, Podlaskie, Poland.