| 735 m|| Slovenia|
The Mirna is a river in southeastern Slovenia. The river, in which the marathon swimmer Martin Strel first learned to swim, is a right tributary of the Sava River in the province of Lower Carniola. It is 44 kilometers (27 mi) long, starts below the settlement of Velika Preska, flows through the Mirna Valley and joins 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.
Mirna (Sava) Wikipedia
The name Mirna is derived through dissimilation from the verb *nyrati 'to arise from the ground'. This is attested by medieval transcriptions of the name containing the letter n (e.g., inter fluenta Nirine in 1016).
The upper part of the river is sometimes named Mirnščica or Mirenščica. The expert on Slovene language Ivan Gregorčič and the geographer Maja Topole have characterised the latter form as incorrect.