a river in Tambov and Riazan’ oblasts of the RSFSR; a left tributary of the Moksha River (Volga basin). The Tsna is 451 km long and drains an area of 21,500 sq km. It flows northward through the Oka-Don Plain. The river is fed primarily by snow. High water occurs in April or early May. The average flow rate 139 km from the mouth is 46 cu m per sec. The river usually freezes over in November or December, but its upper course sometimes remains open until January. The ice breaks up in late March or April. A hydroelectric power plant is situated on the river, and there is local navigation. The cities of Kotovsk, Morshansk, Tambov, and Sasovo are on the river.

a river in Kalinin Oblast, RSFSR; a tributary of Lake Mstino. The river is 160 km long and drains an area of 4,420 sq km. It rises in the Valdai Hills and flows through the Vyshnii Volok Reservoir before emptying into Lake Mstino. The Tsna is fed by mixed sources, mainly snow. The mean flow rate 38 km from the mouth is 12.3 cu m per second. The river freezes between November and January, and the ice breaks up in March or April. The Tsna is used for timber flotation.