The presence of invasive species in river ecosystems poses a constant threat to native biodiversity. In the Basque Country, the Basque Water Agency (URA) has focused on one of the most aggressive: Fallopia japonica, commonly known as Japanese bamboo , a plant that spreads rapidly along riverbanks and displaces native vegetation.
URA has recently completed a series of projects on two sections of rivers in Bizkaia: the La Calera River as it passes through Lanestosa and the Ballonti River between Ortuella and Portugalete. These projects, part of the ongoing conservation of public water resources, are co-financed by the European Regional Development Fund (ERDF) under the Basque Country's 2021-2027 program.
Actions on the La Calera and Ballonti rivers
Along the La Calera River, work has been carried out along a 2.364-meter stretch , from the town of Lanestosa to the border with Cantabria. The area affected by Japanese bamboo in this zone totaled 676 square meters, which have been treated using mechanical and chemical eradication techniques. Meanwhile, along the Ballonti River, work has been carried out on a one-kilometer stretch, encompassing both banks: the right bank in Ortuella and the left bank in Portugalete, near the well-known roundabout with the pipes. The area of ​​Fallopia removed in this second location was 283 square meters.
The main objective of these efforts is not limited to the elimination of the invasive plant. URA has also revegetated the treated areas with native riparian species , such as willows, alders, and ash trees, to restore the ecological balance of the environment. Japanese knotweed (Fallopia japonica) is particularly difficult to eradicate due to its extensive rhizome system, which can reach several meters deep and easily regrow if not completely removed.
Control and monitoring methods
URA teams have combined the manual removal of rhizomes with the controlled application of selective herbicides, always under strict environmental protocols. Eradication is considered successful when the cover of native species completely replaces the invasive one , a process that may require several seasons. In fact, a review is planned for the end of this year to determine if it is necessary to repeat the interventions in any of the sections.
European funding and climate commitment
These actions fall within the scope of the routine environmental maintenance that URA carries out on the Basque river network. Furthermore, ERDF co-financing links this work to the objectives of the Greener Europe program , which aims to combat climate change and preserve the functionality of aquatic ecosystems. Combating invasive species such as Japanese bamboo is a priority for the authorities, as its uncontrolled spread can alter the hydrological regime and reduce the capacity of rivers to mitigate flooding.
The experience gained in Bizkaia will serve as a reference for future interventions in other river basins in the Basque Country. The combination of mechanical, chemical, and ecological restoration methods has proven effective , although experts warn that long-term monitoring is necessary to prevent resurgence. Meanwhile, residents of the affected areas are already beginning to notice the recovery of riverside landscapes, with the return of native birds and plants that had disappeared.
