Press release

Court ruling puts the final nail over Montijo airport plans in major win for the Tagus estuary 

26 April 2026

The Administrative Circle Court of Lisbon issued last week its decision in the legal case against plans to build Lisbon’s new airport in the Tagus estuary, one of Europe’s most important wetlands and a vital stopover for migratory birds, by declaring the expiry of the procedure due to the lapse of the project’s Environmental Impact Declaration (EID).

While the ruling may still be subject to appeal, it is clearly a significant and welcome outcome for the protection of one of Portugal’s most important natural areas.

Lawyers for ClientEarth and Sociedade Portuguesa para o Estudo das Aves (SPEA, BirdLife Portugal), together with ten Portuguese environmental organisations, had brought legal action in 2020 to stop plans for the new airport in the Tagus estuary, Portugal’s most important natural areas.

The case challenged the environmental approval granted to the Montijo airport project, arguing that the Portuguese authorities had failed to properly assess its severe impacts on protected migratory birds and habitats before allowing it to proceed. It also raised concerns about the project’s wider transboundary effect, as it would have undermined the connectivity of migratory routes between Africa and Northern Europe and jeopardise the ecological coherence of the Natura 2000 network.

The Tagus estuary, near Lisbon, is one of the major estuaries in Western Europe and Portugal’s most important wetland for waterbirds. The area affected by the airport project is protected under EU Natura 2000 legislation as a Special Protection Area for birds and a Site of Community Importance, as well as under the Ramsar Convention and as a Portuguese Nature Reserve.

The plans sparked national and international protests from scientists, environmental organisations and the public. In 2024, as pressure mounted against plans to build the new airport in Montijo, the Portuguese government announced it would abandon the project and instead pursue an alternative location near Alcochete, acknowledging that Montijo was not viable from an environmental and biodiversity perspective.

This latest court ruling confirms the legal and environmental flaws at the heart of the Montijo project.

Soledad Gallego, Director of ClientEarth Spain and Mediterranean, said: 

“The Tagus estuary is a site of enormous ecological value for Portugal and Europe, and this ruling is a crucial step towards its protection. Its importance is inherently transboundary, as it supports migratory birds moving between Africa and Northern Europe.”

Julieta Costa, Head of Terrestrial Conservation/ Coordenadora do Departamento Terrestre at SPEA, commented: 

"This decision proves that environmental law is not merely for show: it exists, it is clear, and it must be respected. Legal instruments such as environmental assessments, especially when protected natural sites, like the Tagus estuary and its precious biodiversity, are concerned are essential because they ensure that decisions are based on rigorous, transparent and up-to-date evaluations.” 

The environmental groups launched their legal challenge in 2020, arguing that the Montijo airport’s project breached both EU and national law. Under EU law, projects likely to affect protected sites must undergo a full and reliable assessment before they can proceed. Only where there are no alternatives may exceptions be considered, and even then, strict safeguards and compensation measures are required.

The groups argued that the Portuguese authorities had not carried out reliable assessments and had instead suggested that affected birds could simply be displaced to nearby restored areas – an approach incompatible with EU nature law.

ENDS

Notes to editors:

The Portuguese environmental organisations supporting the legal action by SPEA and ClientEarth are: Liga para a Protecção da Natureza (LPN), Associação Natureza Portugal (ANP|WWF), ZERO - Associação Sistema Terrestre Sustentável, Fundo para a Protecção dos Animais (FAPAS), Grupo de Estudos de Ordenamento do Território e Ambiente (GEOTA), Associação de Defesa do Património Cultural e Ambiental do Algarve (Almargem), and Associação Cristã de Estudo e Defesa do Ambiente Cruzinha (A Rocha) and Quercus.

The case has also been supported by international experts and organisations including the Royal Society for the Protection of Birds (RSPB), BirdLife International and BirdLife Netherlands.

Background

In January 2020, the Portuguese Environment Agency approved the EID for the Montijo airport project.

In June 2020, ClientEarth and SPEA, together with nine Portuguese environmental organisations, filed a legal challenge before the Administrative Circle Court of Lisbon. They argued that the Environmental Impact Declaration for Montijo airport, which approved the project on the basis of a number of assessments, was contrary to national and EU law and should be annulled.

An Environmental Impact Declaration is the formal document setting out the government’s assessment of a project’s environmental effects. EU law requires a series of assessments to determine a project’s impact on protected sites. When a Natura 2000 site is concerned, a project may only proceed where those assessments show that it will not harm the site.

Exceptions are only possible where there are no alternatives, and in such cases the authorities must provide adequate measures to compensate for the damage caused.

The Tagus estuary regularly hosts up to 200,000 wintering birds and is Portugal’s most important site for wintering ducks, waders and other waterbirds such as flamingos and gulls. During migration periods, it can host more than 300,000 birds, serving as a crucial stopover site on long migratory journeys.

About ClientEarth

ClientEarth is a non-profit organisation that uses the law to create systemic change that protects the Earth for – and with – its inhabitants. We are tackling climate change, protecting nature and stopping pollution, with partners and citizens around the globe. We hold industry and governments to account and defend everyone’s right to a healthy world. ClientEarth teams in Europe, Asia and the USA work to shape, implement and enforce the law, to build a future for our planet in which people and nature can thrive together.