The largest rivers in the Harz are the Innerste, the Oker and the Bode in the north; the Wipper in the east; and the Oder in the south. The Innerste merges into the Leine and its tributaries are the Nette and the Grane. The rivers Radau, Ecker and Ilse all discharge into the Oker. The Hassel, the Selke and the Holtemme (whose main tributary is the Zillierbach) flow into the Bode. The Wipper is fed by the Eine. The Rhume is joined by the Söse and the Oder; the latter being fed by the Sieber. The Zorge, the Wieda and the Uffe all flow into the Helme.