"We have eliminated something that for us it was imperative to have, at this time, in these two subjects, on the issue of the sedimentary impact and coastal erosion and water quality, we understand that we have grounds and conviction to understand that the extension of the breakwater does not represent any danger to what we want to do, which is to put Blue Flags on the beaches of the city of Porto," said Frederico Fernandes, referring to an international mark of quality for beaches.

Fernances said that studies commissioned by a working group from the University of Porto, University of Aveiro and "other technical specialists" set up to monitor the project, were clear.

The deputy mayor of Porto, Filipe Araújo, also said there was "unanimity" among experts and the findings of an environmental impact study on coastal erosion, that the phenomenon will not "be aggravated" by the breakwater’s extension.

According to Araújo, a review of the various studies on the project made it possible to conclude that a recent "increase in pollution" continues to be related to an issue that, in his view, "should concern everyone" – outflow from the Riguinha rivulet.

"What exists at this moment that should concern us all in that water basin is indeed a problem that is the … Riguinha, aboutwhich the municipality of Porto has for some years been warning [that we need] a solution that satisfies the use of the international beach in Matosinhos all the year," he stressed.

He also noted that the monitoring group, on which the councils of both Matosinhos and Porto are represented, as well as the ports of the Douro, Leixões and Viana do Castelo, the Portuguese Environment Agency (APA) and other groups, will "require that a series of measures be implemented" in this context, with the decontamination of the Riguinha one of these.

According to Araújo, the studies commissioned by the working group are soon to be made public, as well as those of the ports management company APDL.

In February, Portugal’s minister for the sea, Ana Paula Vitorino, announced an investment of about €217 million, the bulk of it public money, in the port of Leixões between now and 2023, to boost its competitiveness. The contracts involved include the extension of the breakwater by 300 metres, the deepening of the entrance channel and other major works, including the creation of a new terminal on the south jetty.

However, the plans have drawn criticism from the political parties, councils, surfers and local residents, with a ‘Say No to the Wall’ movement organising a petition and demonstration against the breakwater project in particular.

In March, the municipality of Matosinhos approved a document in which it argues that the contract for the works at Leixões should not be awarded until the final overall project and environmental impact assessment have been presented. However, the assembly rejected a proposal to request the suspension of the public tender.

The APDL, for its part, has pledged that the longer breakwater "will not end the waves or surfing, nor will it turn the beach into a lake" – as some locals and surfers fear.