In which European country is the Mirna River (also known as the Sava River) located?

The Mirna River is a river in southeastern Slovenia. The river is a right tributary of the Sava River in the province of Lower Carniola.

Its length is 44 kilometres (27 mi) long, starting below the settlement of Velika Preska, it flows through the Mirna Valley and joining the Sava at Dolenji Boštanj, opposite Sevnica.

The largest settlement on the river is Mirna. The river is traversed by the Sevnica–Trebnje Railway. The river was mentioned for the first time in 1028 in relation to a 1016 document by Henry II, Holy Roman Emperor.

Interestingly, the name of the river, 'Mirna' is derived through dissimilation from the verb 'nyrati', which means to 'to arise from the ground'. This is attested by medieval transcriptions of the name.

The famous Slovenian marathon swimmer, Martin Strel first learned to swim in this river. Strel holds successive Guinness World Records for swimming the Danube river, the Mississippi River, the Yangtze River, and the Amazon River.