The principal river is the Drave, which flows from west to east through the length of the duchy, and receives in its course the waters of all the other streams, except the Fella, which reaches the Adriatic by its junction with the Tagliamento.
To the north of the valley of the Drave the duchy is occupied by the Hohe Tauern and the primitive Alps of Carinthia and Styria, which belong to the central zone of the Eastern Alps.
A relative scarcity in running waters prevails in the whole region between the Danube and the Drave.
The first consists in the parallelism in the course of its rivers, as the Danube and the Theiss, the Drave and the Save, the Waag with the Neutra and the Gran, &c. The second is the direction of the rivers, which converge towards the middle of the country, and are collected either mediately or immediately by the Danube.
The country south of the Drave is occupied by several groups of the southern limestone zone, namely the Carnic Alps, the Julian Alps, the Karawankes and the Steiner Alps.