a river in Tula Oblast, RSFSR; a right tributary of the Oka River of the Volga River basin. The Upa is 345 km long and drains an area of 9,510 sq km. Its course is located within the Central Russian Upland. The river describes large loops and is fed primarily by snow. High water is from late March to early May. The mean flow rate 89 km from the mouth is 40.2 cu m per sec. The Upa freezes over in late November or December (sometimes in January), and the ice breaks up in late March or April. The river is a water supply source. The cities of Sovetsk and Tula are located on the Upa. A reservoir near Sovetsk has an area of 5.7 sq km.