This project aims to pave the way to remove 8 barriers to restore 143.4 km of river connectivity, freeing up the entire course of the Oeiras River (from its source to its outlet in the Guadiana River), enhancing habitat, range, and abundances of several native, protected/endangered fish and mussel species and the overall ecological status of the river.
The Oeiras River is in the western part of the Algarve and is one of the tributaries of the Arade River. It flows through various rural areas, passing through agricultural zones and small towns before joining the Arade River. It is a typical intermittent Mediterranean stream and is home to several native and endangered species, including three freshwater mussels (Unio tumidiformis, Anodonta anatina, Unio delphinus), their host Squalius spp., and the migratory eel (Anguilla anguilla). The area is also home to iconic mammals, such as the Iberian lynx (Lynx pardinus) and the otter (Lutra lutra).
| Project status | Completed |
|---|---|
| Project type | Dam removal: pre-demolition |
| Country | Portugal |
| River | Oeiras |
| Focal species | Swollen river mussel (Unio tumidiformis), two other native mussel species (Duck mussel: Anodonta anatina; Dolphin freshwater mussel: Unio delphinus), several chub species (Squalius spp.), Southern Iberian barbel (Luciobarbus sclateri), Iberian arched-mouth nase (Iberochondrostoma lemmingii), Iberian lynx (Lynx pardinus), Otter (Lutra lutra) |
| Organisation | ANP/WWF |
| Website | ANP/WWF |
The Institute for Nature Conservation and Forests (ICNF) and the company Somincor contacted ANP|WWF to investigate the potential to remove 9 barriers they had identified in the Oeiras River, thereby restoring 143.4 km of its connectivity, improving its ecological status and providing habitat for several native fish and endangered freshwater mussels. At the same time, the return of other threatened fish previously found in the river (e.g. the freshwater blenny Salariopsis fluviatilis, larger individuals of barbel, and the marine lamprey Petromyzon marinus) could be encouraged. An added value of this project is the Conservation Plan for the Oeiras River mussels, developed by Somincor, which includes the restoration of river habitat in specific pools in upstream areas of the mine. This project constitutes a rare opportunity to work closely with local authorities and a company to contribute to mitigating its impacts on the environment while restoring rivers.
This project aims to pave the way for removing 8 barriers on the Oeiras River, in addition to the removal planned in another Open Rivers Programme grant. In total, these removals have the potential to restore 143.4 km of river connectivity and significantly improve the habitat for, and thus contribute to the conservation of, biodiversity and the ecological status of the river.
To complete the proposed work, ANP|WWF will undertake several activities, including feasibility assessments, engaging the local community and key stakeholders, providing environmental education sessions, and disseminating the project’s results. These efforts will raise awareness and advocacy for dam removals both locally and nationally, promote knowledge exchange, and potentially lead to increased funding for further dam removals in Portugal. Opportunities will also be explored to scale up the project to the Vascão River, which is already targeted by another project recently submitted to the WWF’s “Rivers2Restore” initiative.
Somincor will continue to monitor fish and freshwater mussel communities, as well as water quality, allowing us to assess changes in the distribution and abundance of fish and mussels, and in water quality, following the removal.
The project aimed to prepare for the removal of eight barriers along the Oeiras stream, with the objective of restoring 143.4 km of free-flowing river. Its activities focused on feasibility assessments, stakeholder engagement, and the development of technical removal plans.
Field visits were carried out in October 2024 and March 2025, followed by a public presentation on 28 May 2025 in Mértola, attended by 27 participants including municipal representatives, technicians from ICNF (Institute for Nature Conservation and Forests) and APA (Portuguese Environment Agency), local associations, landowners, and researchers. This process fostered a stronger understanding of the ecological, cultural, and socio-economic roles of barriers in the Oeiras stream and promoted open dialogue among diverse actors. The work also led to the identification of significant ecological risks, such as the potential loss of endangered freshwater mussel populations, and highlighted the social opposition linked to removing barriers with cultural and ecological value.
One barrier will be removed through a follow on demolition grant from the Open Rivers Programme.
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