The Bidasoa (Bidassoa) is a river in the Basque Country of northern Spain that runs largely south to north. Named as such downstream of the small town of Oronoz-Mugairi (municipality of Baztan) in the province of Navarre, the river actually results from the merge of several streams near the village Erratzu, the stream Baztan that rises at the north-eastern side of the mount Autza (1,306 m) being considered the source of the Bidasoa. It joins the Cantabrian Sea (Bay of Biscay) between Hendaye and Hondarribia.
The river is best known for establishing the borderline at its lower tract. This stretch is crossed not only by aircraft at low height but by important European communication axes, namely AP-8 E-5 E-80 E-70 A-63 (motorway), main roads N-1 N-10 (connection at Saizar) and major railways (connecting the ADIF and SNCF networks). Besides these major lines, other regional ones cross it too, eg regional railway Euskotren (terminal in Hendaia) and another double bridge (pedestrians/vehicles) joining the towns on the border, ie the historical Santiago Bridge (Way of St. James). At this stage of the river, urban landscape prevails (built-up area).
Before pouring its waters into the ocean, it forms a bay called Txingudi located between these towns and Irun, the site being designated Wetland of International Importance in 2002, with a total area of 1.28 km2. The banks of Hondarribia hold the minor San Sebastian Airport serving domestic flights and currently mired in controversy over its lengthening and upgrading scheme.
The Bidasoa flows through much of its 66 km length over Navarrese territory, except for the last 10 km, where it establishes the borderline between France and Spain, as well as the boundary between the Basque provinces of Gipuzkoa and Labourd. In line with the distribution of the river's length, the bulk of its watershed's area lies on Navarre (684 km2). The basin holds 105 permanent streams and rivers that number 497 km, the region being drenched in rains regularly. The Navarrese side of the basin (rural landscape) is inhabited by 22,000 inhabitants. 70% of its population have the sewage treated before spilling to the river.
But for the first 15-odd kilometres, the river clings to the north to south disposition of other neighbouring rivers of Gipuzkoa joining the Bay of Biscay, eg Urumea, Oria, etc. Strengthened by the waters harvested from the sides of the pass of Belate, downstream of Doneztebe the river heads north and crosses the town of Bera at the north end of Navarre before entering Gipuzkoa at Endarlatsa. From the town of Doneztebe on, the main road N-121 runs along till the roundabout across the river from the toll of Biriatu by the AP-8 (motorway). Next comes Behobia and the major towns on the shores of the estuary.
The main tributaries of the Bidasoa are the minor rivers Zeberia (length 10,80 km), Ezkurra (20,90 km), Latsa (11,10 km) and Endara (9,90 km). Additionally, further small rivers and streams feed the Bidasoa all along.
The Navarrese tract of the river is a preferred destination for fishing enthusiasts, the river being home to several native fish species, namely eel (Anguilla anguilla), salmon (Salmo palar), trout (Salmo trutta), bullhead (Cottus gobio), Barbatula barbatula, Phoxinus phoxinus, gudgeon (Gobio lozanoi), sea lamprey (Petromyzon marinus), allis shad (Alosa alosa), flounder (Platichthys flesus) and grey mullet (Chelon labrosus), some of them declared endangered species and highly interesting (especially bullhead and salmon). Moreover, a species of the Ebro, ie Chondrostoma miegii, has been introduced in the last 30-40 years on the lower tract of the Bidasoa, thereafter extending gradually upstream.
As a result, overfishing has become a major problem for the river's fauna, with a especial pressure put on big salmons going upstream to spawn. They don't make it to their goal and die before spawning, either falling prey to the fishers' bait or unable to overcome hydroelectric powers stations (128 over all the course) and the 114 related dams, 63% of them preventing migratory fish from achieving their purpose. Schemes by the Regional Government of Navarre are under way with a view to handling the issue.