Szum is a reserve protecting the valley of the Szum Stream and its characteristic small rock rapids. The river forms them by eroding the valley in a calcareous marlites. People used to call hose rapids washers, because they were used for washing laundry. At the bottom of the valley we can find alder trees and a riparian forest, whereas along the river side there is a fir forest and some characteristic mountain plant species in the ground cover.Such rock rapids are a sensation countrywide as they are almost entirely limited to the rivers of the Roztocze area.