West-north-west of Mostar to the bend of the river Narenta, differs in many respects from the larger territory.
West of the Narenta, their flanks are in places covered with forests of beech and pine, but north-east of that river they present for the most part a scene of barren desolation.
The most conspicuous example of these is the Trebinjcica, which disappears in two swallow-holes in Popovopolye, and after making its way by a subterranean passage through a range of mountains, wells up in the mighty source of Ombla near Ragusa, and hurries in undiminished volume to the Adriatic. The Narenta, or Neretva, is the one large river of Herzegovina which flows above ground throughout its length.
North of Mostar, it cleaves a passage through the celebrated Narenta defile, a narrow gorge, 12 m.
In Herzegovina, although many of the high mountain tarns are unproductive, the eel-fisheries of the Narenta are of considerable value.
It then pierces through the mountains of northern Herzegovina, traverses the Narenta valley, and runs almost parallel with the coast to Trebinje, Ragusa and the Bocche di Cattaro.
Small steamers ply on the Drina, Save and Una, but the Bosna, though broad from its very source, is, like the Vrbas, too full of shallows to be utilized; while the Narenta only begins to be navigable when it enters Dalmatia.
The bridge across the Narenta, at Konjica, is said to date from the 10th century.
The only considerable rivers flowing into the Adriatic are the Narenta, Drin and Viossa.