The Jerma (Serbian Cyrillic: Јерма) or Erma (Bulgarian Cyrillic: Ерма) is a river in southeastern Serbia and western Bulgaria. Even though not very long (74 km), it is notable for passing the Serbian-Bulgarian border twice.

Course

Serbia

The Jerma originates in the undeveloped and sparsely populated area of Kraji?te, in the southeastern corner of Serbia. Starting from between the artificial Lake Vlasina and the Bulgarian border, it flows to the northwest on the eastern slopes of the Gramada mountain, passing through the village of Klisura, after which it enters the area of Znepolje (Bulgarian: Znepole; Cyrillic: Знепоље/Знеполе), an arid region stretching over the border into Bulgaria. This is where the Jerma crosses the border for the first time, at the border crossing of Strezimirovci.

Bulgaria

Continuing through the Bulgarian part of Znepolje curving around the eastern side of the Ruy mountain, the river, now called Erma, is also known as Transka reka after the town of Tran, a regional centre of this area. The Erma passes close to the villages of Glavanovtsi and Turokovtsi, where it turns north, running through Tran. After Tran, the Erma cut the famous gorge Transko zhdrelo (”Gorge of Tran”). After the gorge, the Erma receives its major tributary, the Yablanitsa, right before it re-enters Serbia after 26 km of flow in Bulgaria. The river crosses the border for the second time at the villages of Bankya (Bulgaria) and Peta?inci (Serbia).

Returning to Serbia

The Jerma continues to flow generally to the north, passing next to the village of Iskrovci and the picturesque spa of Zvona?ka Banja. Proceeding between the mountains of Greben and Vla?ka planina, it runs close to the villages of Trnsko-Odorovce and Vlasi, and the monasteries of Sveti Jovan, Sveti Nikolaj and Sveta Bogorodica, before it empties into the Ni?ava, southeast of Pirot after a total of 48 km in Serbia (thus belonging to the Black Sea drainage area). In this last section, the Jerma flows through the Sukovo coal basin, named after the village Sukovo, which is not on the banks of the Jerma itself, but a bit to the west. However, despite the hard coal was of high quality (7,000 cal), the coal mine near Pirot was shut down and coal is not being extracted anymore. In this final section, the Jerma is also known as Sukovska reka (Cyrillic: Суковска река; “river of Sukovo”). The river also has potential for production of hydroelectricity, but this resource is not used either.