In a statement, the authority said that the red flag had been raised on the beach after analyses of the sea water carried out by the Portuguese Environment Agency (APA) indicated that the water was "not suitable for bathing”.
Speaking to Lusa, the captain of the port of Lagos, Pedro Fernandes da Palma, said that the red flag had been raised at the end of the morning, prohibiting bathing on this beach in Faro district.
According to the captain, it is not known what caused the contamination, by faecal coliforms, and new analyses are now being carried out by the APA, which will maintain monitoring of water quality.
If the analyses show that the values are within normal parameters, the ban will be lifted, according to the statement from the maritime authority.
The action was articulated between the harbour captaincy and the local command of the Lagos Maritime Police, the Health Authority, the APA and the Lagos City Council.