Three Romanian workers, aged 21, 24, and 40, drowned while carrying out waterproofing work inside a water tank in Quinta do Lago, a locality in southern Portugal.
Aside from the Romanians, three other people received medical attention at the scene.
According to Portuguese publication Notícias ao Minuto, the victims were found dead in the water tank of a private property.
The information was confirmed by the National Republican Guard and the District Command for Relief Operations.
The exact cause of the accident has not yet been established. The local labor inspectorate is set to investigate the circumstances in which the tragedy occurred.