The Acid River was a river on Skaro in and around which Zeg and the Dalek Emperor once battled.
The Dalek Emperor thought that the sulphuric acid would destroy Zeg, so led him onto an overhang above the river. He then shot the overhang, which fell away, and Zeg fell into the river. However, as his casing was made of metalert, the acid could not hurt him, and he emerged unharmed. (COMIC: Duel of the Daleks)