The Jona is a river in the Swiss cantons of Zürich and St. Gallen, forming partly their mutual border, and one of the main tributaries of Obersee, Lake Zurich.

Flowing eastward through a small valley and passing an impressive waterfall, the river changes its direction towards south by a ravine, which is crossed by a viaduct of the Tösstalbahn (operated by the S26 service of Zürich S-Bahn).

It underneaths the Oberland Autobahn (A53 highway), at the same time also reaching the canton of St. Gallen and the Rapperswil-Jona municipality.

It is assumed that the name originates as either Celtic Jauna (the cold one) – the Jona is still largely determined by forest area – or, as Indo-European yamam, meaning stream.

Latest interpretations say that the Indo-European word jeu roughly means to move, followed by the Old High German name Jouna .