The Meža is a 43 kilometres (27 mi) long river in Carinthia, Slovenia. It has its source on the Austrian side of the state border near Mount Olševa, becomes subterranean a kilometer from its source, and reappears on the surface in Koprivna near Črna na Koroškem, Slovenia. It is the central river of the Mežica Valley. It flows through Črna na Koroškem, Mežica, Prevalje, and Ravne na Koroškem, and into the Drava River at Dravograd. In its first part the Meža falls rapidly and is a typical alpine river with its tributaries from the Kamnik Alps and the Karavanke Mountains. After Črna na Koroškem it becomes a slow meandering lowland river. Its main tributary is the Mislinja River, which joins the Meža River a couple of hundred meters before it joins the Drava.
The Meža is noted for being the most polluted river in Slovenia. In 1982 the singer-songwriter Marijan Smode wrote a song about it titled Mrtva reka (The Dead River). This song has even been published in primary-school textbooks. The main polluter has been the Ravne Steelworks (Slovene: Železarna Ravne) conglomerate.