Perofilho Weir, Portugal

Perofilho Weir removal will boost local biodiversity

The Perofilho stream

The Perofilho stream is located within the Rio Maior hydrographic basin, which is a tributary of the Tejo River. It is of great ecological importance as it provides critical habitats for migratory fish species and supports a variety of other aquatic animals, like the Iberian painted frog (Discoglossus galganoi) and otter (Lutra lutra). Some of the fish species inhabit Perofilho stream are critically endangered, like the European eel (Anguilla anguilla) and the Portuguese arched-mouth nase (Iberochodrostoma lusitanicum).  

The Perofilho Weir

Perofilho Weir was constructed in 1978 for irrigation purposes but has remained obsolete for a long time. This 1.7-m high and 3-m wide concrete structure (Figure 1) was the only barrier disrupting the natural flow of the Perofilho stream, severely hindering fish migration, especially for the critically endangered European eel and other vital freshwater species. The weir was owned by the SOS Animal Association, and its removal was a key step toward restoring the stream’s ecological balance. With the full support of the Municipality of Santarém and authorization from the Portuguese Environment Agency, this project marked a significant milestone in preserving local biodiversity and enhancing the health of the river ecosystem.  

Figure 1. Looking downstream of the Perofilho Weir, Perofilho stream, Santarém, Portugal © Fábio Pinto | WWF Portugal

Barrier removal

The Perofilho Weir removal project officially began in February 2023, with meetings and discussions among relevant stakeholders. Obtaining the necessary removal permit from the Portuguese Environment Agency was very time consuming, and adverse weather conditions in March 2024 postponed the weir demolition to autumn of the same year. Prior to the removal works, invasive plants species were removed and ichthyological surveys were carried out. The in river works begun on September 21 (Figure 2, Video 1) and were completed a week later (Figure 3, Video 1).  

Figure 2. Removal works of the Perofilho Weir, Perofilho stream, Portugal © Fábio Pinto | WWF Portugal

Figure 3. The Perofilho Weir site following the completion of the demolition works © Fábio Pinto | WWF Portugal

The project was led by WWF Portugal in cooperation with the Municipality of Santarém and SOS Animal Association. Princeton Hydro was involved in the designing of the removal works. The project costed ~27000 € and was supported by the European Open Rivers Programme. The local community also strongly and actively supported the project.  

Video 1. Demolition works of the Perofilho Weir in September 2024 © WWF Portugal

Following the weir demolition, restoration measurements were taken. A vegetated biodegradable timber wall was built on the one bank and parts of the concrete weir were placed on the riverbed and the banks to secure their stability (Figure 4). Native willows were also planted on the banks to further stabilize them in the long run (Figure 4).  

Figure 4. Planting native tree and shrub species on the banks of Perofilho stream, following the demolition of the Perofilho Weir © Fábio Pinto | WWF Portugal

Challenges

The project faced key challenges, including delays in obtaining permits and adverse weather conditions, particularly heavy rainfall, which postponed the demolition. Additionally, there were initial difficulties in building trust and cooperation between stakeholders. However, the project was granted an extension until September 2024, and through increased meetings and collaboration, these challenges were successfully overcome, paving the way for the project’s eventual success.  

Ecological and community benefits

The removal of the Perofilho Weir restored 2.5 km of river, enhancing habitat connectivity for native aquatic species, especially endangered ones, like Anguilla anguilla and Iberochodrostoma lusitanicum. The project also fostered strong community involvement, with educational sessions at local schools raising awareness about the importance of removing obsolete barriers. Moving forward, post-removal monitoring of fish populations will be conducted with support from the Agronomy School of the University of Lisbon. 

Watch a live interview from the former Perofilho Weir site:

Before & After photo pair

The restored site at Perofilho Weir (left) before and (right) after the removal works © Fábio Pinto | WWF Portugal 

With many thanks to José Pedro Ramião from WWF Portugal for providing the information and the visuals presented herein.

Prepared by Foivos A. Mouchlianitis