Together with the Vydra, which is its main source, the Otava is 134.8 km (83.8 mi) long, making it the 13th longest river in the country.

A possible but unproven origin is the Germanic word Vatahva, meaning "quick water".

The Otava itself is formed by the confluence of the Vydra and Křemelná in the territory of Hartmanice, and is 111.7 km (69.4 mi) long.

[3] The Otava has many relatively significant tributaries, the following being the longest ones:[4] The largest settlements on the river are the towns of Písek and Strakonice.

The river flows through the municipal territories of Hartmanice, Rejštejn, Dlouhá Ves, Sušice, Dobršín, Rabí, Žichovice, Velké Hydčice, Malý Bor, Horažďovice, Střelské Hoštice, Horní Poříčí, Katovice, Strakonice, Slaník, Přešťovice, Štěkeň, Čejetice, Putim, Kestřany, Písek, Čížová, Vrcovice, Vojníkov, Vráž, Ostrovec, Oslov, Varvažov and Zvíkovské Podhradí.