Freeing 1/3rd of the Sousa River to recover endangered, migratory fish species

This project aims to pave the way for the removal of 13 barriers along the Sousa River, starting from the most important one, the one closest to the sea.

Introduction

The Sousa River is part of the lower Douro Catchment and is considered very important and recommended for restoration. It is a sanctuary for local freshwater fauna and diadromous migratory fish because the river mouth is located downstream of the first large dam on the Douro River, the Crestuma-Lever Dam (Douro Vivo report). It is thus critical that the barriers and dams on the lower section of the Sousa River are permeable to fish i.e. removing useless and obsolete barriers.

The Sousa is a highly degraded river due to multiple stressors related to human activities. It has suffered over the last centuries from urban, agriculture and industrial pollution. The presence of many barriers and large weirs also contributed to the fragmentation, isolation and extirpation of fish and the once massive populations of the critically endangered freshwater pearl mussel Margaritifera margaritifera present in this river. Nevertheless, the water quality in this river system has been increasing substantially over the last two decades since the inception of wastewater treatment plants in major urban centres and industries.

At a glance

CountryPortugal
RiverSousa
Key habitatsRiver and scrubland
Focal speciesAnguilla anguilla, Petromyzon marinus, Alosa alosa, Margaritifera margaritifera, Salmo salar, Acipenser sturio, Lutra lutra
Project typeBarrier identification and prioritisation
Project statusLive

Project context and opportunity

According to a report made by the University of Trás-os-Montes for GEOTA as part of the MAVA-funded project Douro Vivo, the Sousa River contains 81 obstacles. This project aims to pave the way for the removal of 13 weirs on the Sousa that were also prioritised for removal by the ministerial report, with a potential of restoring 21 kms of river, amounting to one third of the river’s length.

These removals will enhance the conservation of several migratory species of conservation concern, such as lamprey, eel, and shad. The removals may also lead to recreating conditions for the come back of other migratory locally extinct species, like the Atlantic salmon and sturgeon, and the once hosted and critically endangered freshwater pearl mussel. Other native fish species of conservation concern will also be benefited, as well as iconic mammals such as the otter. The project is expected to benefit from ongoing dam removal projects, such as the ‘Galaxes’ weir and the ‘Perofilho’ weir. This will strengthen existing relationships and build new partnerships in the catchment and engage local communities, creating awareness about the benefits of removing dams.

Project aims

This project aims to prepare the path to remove 13 barriers along the Sousa River, starting from the most important one, the one closest to the sea, which is expected to set a precedent and lead to the removal of the other 12 barriers in due time. This will open up ~21 km of Sousa River, considerably enhancing the conservation of several migratory fish species and other biodiversity. The project will also restore a better ecological status of the river, which was highly degraded in the last few decades due to multiple stressors related with human activities, as well as improve/promote several recreational activities, such as fishing, hiking, kayaking and local tourism which could be enhanced by the return of migratory fish.

The project aims to involve the Municipality of Gondomar, the local Parish Councils, local fishing associations, APA, ICNF, researchers from the CIBIO that participated in the Douro Vivo project, and local construction companies with experience in the demolition of weirs. Activities will consist of field visits to the barriers, confirmation of their owners, studies on the feasibility of removing all the barriers, meetings with local community and the Municipality of Gondomar to discuss the removals, securing the necessary authorisations, contracting a construction company to prepare demolition and river design plans and provide invoice estimates, application for funding the removals, and efforts to secure co-funding from existing legislation or strategies.

Partners

ANP

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WWF