In fact the major river in eastern Boiotia (central Greece), flowing eastwards from the foothills of Mt. Helikon, forming the boundary between Thebes and Plataia and emptying into the strait of Euboia near Oropos. See Pausanias 9.4.4 (web address 1).
There was also a river of this name in the NE Peloponnese (Pausanias 2.5.2-3; web address 2). Pausanias reports that the Phliasians and the Sikyonians who lived in the area thought that the river originated in Anatolia as the Maeander and followed an underground route to their territory where it surfaced as the Asopos. See also Pausanias 2.7.3 (web address 3) and 2.7.9 (web address 4). Sharing the name were also a river in (?)Pisidia and a town in the SE Peloponnese (Pausanias 3.22.9, web address 5).