The protection zone of the Biebrza National Park surrounds the highly bio-diversified and most unique Biebrza River. Its headwaters are located in the small moraine hills of Sokolskie, just south of the small and quaint village of Nowy Dwór. The length of the Biebrza River is 164 km, draining its waters into the larger Narew River at the village of Ruś. Only 10 km is excluded from the boundaries of the Biebrza National Park; with a catchment area of over 7000 square kilometers the Biebrza Valley is considered one of the largest catchment areas in Poland surpassing many man made reservoirs. The Biebrza and the Nieman catchments are connect by the Augustowski Channel a hydro-technical achievement of the 19th century. This and many other drainage works contributed to the lowering of the local ground water table. The Biebrza Marshes are supplied by two ways its water table and the tributaries that discharges into the Biebrza. The majority of Biebrza`s tributaries flowing into its waters come from the right bank, these include the Lebiedzianka, Netta, Koptkówka, Jegrznia, Dybła, Ełk, Klimaszewnica and the Wissa streams. The tributaries of the left bank contributes only 24.5% of the Biebrza`s outflow and these streams include the Sidra, Brzozówka, Biebła Czarna Struga and the Kosódka. From the headwaters to the river mouth the average elevation decline is 36%, but taking into consideration that the surface area of the valley, due to its flooding, this decline can be reduced to 19%. An average yearly flow of 27,5 m3/s was measured at the southern basin village of Burzyn. Snow thawing in spring is the primary reason for floodings that time of the year, these floodings contribute to the valley`s highly bio-diversified and habitat mosaic landscape.