The Titarisios (Greek: Τιταρήσιος, formerly Ξεριάς - Xerias) is a river in Thessaly, Greece.

[2] The river begins at the western slopes of Mount Olympus and flows southwest, then south.

The wetlands of the Titarisios are threatened by uncontrolled waste disposal, for instance near the villages Rodia, Vryotopos and Deleria.

Mati is today the only natural lake in Thessaly and although it has only a small area (25 ha) it is the core of an ecosystem with rich flora and fauna.

Several types of vegetation are found along the river Titarisios: Specific studies of the fish in the Titarisios river have not been done, but 37 species of fish have been reported, and another 11 species are presumed present.