Perofilho Weir, Portugal

Introduction

Flowing within the Tagus Catchment, the Perofilho Stream is a short, 6.6 km long, tributary of the Tejo River. It flows into the hydrographic Rio Maior basin, in a river locally known as Azambuja River or Rio Maior.

The Perofilho Weir is within private land belonging to the SOS Animal Association. The land was acquired recently by the association, and the association aims to realise beneficial environmental projects there. Important freshwater biota has been observed along or near the Perofilho Stream inside the property, such as the migratory and critically endangered eel, the Eurasian otter, and the Iberian painted frog.

Project context and opportunity

This weir removal project arose thanks to the strong relationship between ANP/WWF, the local municipality, and the land owner. Such good political and local support is expected to boost advocacy for dam removal nationally. Moreover, the relevant ecological benefits of removing this weir, such as habitat recovery for eels and otters, will continue to strengthen dam removal advocacy over time. The project team is also eager to conduct fish sampling in the stream to detect other fish species of conservation concern.

Project aims

This removal will improve the water quality and Water Framework Directive Status (currently listed in in Poor state) of the stream, bringing positive effects for the conservation of native fish, amphibians and mammals. It will restore fluvial connectivity for 2,5 km of stream (almost half of its entire course) and potentially more, improving the connectivity between this river and the lower stretches going into the Tejo River. This demolition could also pave the way for other barrier removals in the same stream and in the Tejo Catchment (in total from the Perofilho Weir up to the confluence in the Tejo River it is 34 km), improving habitat for several autochthonous fish species present in the Rio Maior hydrographic basin.

In addition the project will result in the first research into fish species in this stream. Recently, an eel was observed downstream of this barrier, indicating the presence on this critically endanger migratory fish species. Fish monitoring through electrofishing and/or fish nets and eDNA collection will allow the project team to collect more robust data, creating a better understanding of local fish populations and documenting possible improvements in fish and macroinvertebrates abundances after the removal. In particular, possibilities will be sought to perform a citizen science project focussed on eels in this river and possibly the whole Tejo Basin.

Project achievements

The Perofilho weir removal project has delivered significant ecological, social, and collaborative benefits, demonstrating the importance of restoring free-flowing rivers and enhancing freshwater biodiversity. Below are the key achievements of the project, led by ANP/WWF in partnership with SOS Animal and the Santarém Municipal Council:

• Ecological Restoration: The removal of the Perofilho weir restored 2.5 km of stream connectivity, improving habitat conditions for freshwater biodiversity, including the endangered Portuguese arched-mouth nase. Post-removal rehabilitation activities further stabilised riverbanks and the riverbed through the planting of native tree species and the installation of live alder stakes.
• Community and Stakeholder Engagement: The project successfully strengthened local community engagement through outreach initiatives, including the organisation of an environmental education session with local students. The session highlighted the environmental benefits of removing obsolete river barriers and the challenges posed by keeping fluvial blockages in place. The final event brought together 40 participants, including members of the local community, researchers, and authorities, fostering dialogue on dam removal and building momentum for future efforts.
• Partnership Building: The project deepened relationships with key stakeholders, such as the Portuguese Environment Agency, and helped boost the dam removal movement in Portugal. This was the third dam removal undertaken by civil society, setting a strong precedent for future initiatives.
• Policy Influence: Following the publication of the River Restoration Policy Brief (in Portuguese), ANP/WWF shared the document with decision-makers, government agencies, and institutions. This helped raise awareness and encourage stakeholders to prioritise dam removal in their policy agendas.
• Communication Impact: The project achieved exceptional visibility, generating 25 national and local media articles, as well as 20 social media posts and stories across multiple platforms. These posts reached 55,697 viewers, the highest reach ever for ANP/WWF in an Open Rivers Programme project!

Through these achievements, the Perofilho weir removal project has not only restored an important aquatic ecosystem but also built a strong foundation for future dam removal efforts in Portugal and beyond. The project was completed in December 2024.