The Tosna is a northward river in Luzhsky, Tosnensky, and Kirovsky Districts of Leningrad Oblast, Russia, as well as in the city of Saint Petersburg. It is a left tributary of the Neva. The towns of Tosno, Nikolskoye, and Otradnoye, as well as the urban-type settlement of Ulyanovka are along it. Its length is 121 km. Its drainage basin covers 1640 km2 which mainly has northward flowing streams. Its main tributary is the Yeglinka which is on the left bank. The source is in swamps south of the settlement of Radofinnikovo. The river flows north, enters Tosnensky District, passes the town of Tosno, and essentially enters the suburbs of Saint Petersburg. There, it flows through Ulyanovka and Nikolskoye. In this area, limestone rocks occasionally form the banks. In particular, Sablinskiye Caves, disused quarries, are by the river. A stretch of Tosna between Nikolskoye and Otradnoye serves as a border between the city of Saint Petersburg (west) and Leningrad Oblast (east). The mouth/confluence abuts the west of Otradnoye, a town.