The source of the Krupa River is the largest and one of the most beautiful and biologically most important karst springs in Bela krajina. When the flow is high, the river flows from under the 30-meter high rock wall at the rate of 1,000 liters per second. The spring is the habitat of the cave salamander (Proteus Anguinus) and the only known habitat of congeria kusceri cave mussel in Slovenia.