Tyosha (Russian: Тёша) is a river in Nizhny Novgorod Oblast in Russia, a right tributary of the Oka River. The length of the river is 311 km. The area of its basin is 7,800 km². The Tyosha freezes up in November - first half of December and stays icebound until the second half of March - first half of April. Its biggest tributary is the Seryozha River. The city of Arzamas is located on the Tyosha River.