The river results from the union of various streams in Urdazubi (Navarre), going on to cross the Spanish-French border at Dantxarinea after 14 kilometres (8.7 mi) meandering across Navarrese soil.

For all its shortness, the river takes on several names in Basque language at different stretches of the course, e.g. Sarrakaria, Urma, Uhertsi (spelled sometimes Ur Ertsi), besides the above Ugarana and Urdazuri.

This conspicuous diversity reflects the historic situation of the native language, deprived of official recognition whatsoever or transmission through formal schooling up to recent times (and still).

The geographical situation of the basin makes its climate mild (average temperature 14 °C) under the influence of humid air masses blowing from the sea.

Yet the clash between these air currents and the Pyrenean region spurs sudden showers frequently (average annual rainfall on the watershed 2,000 mm).