Four people were injured when the suction hopper dredger Brasinho overturned and sunk off the Ria Formosa island of Armona, Portugal.
The 80-metre dredge owned by the Faro-based dredging company Sofareias was carrying out a sand nourishment operation when it toppled, leaving the four workers in the water.
Autoridade Maritima Nacional (AMN) said the crew were rescued by a water taxi but were suffering from hypothermia. AMN said one crew member suffered a spinal injury.
Brasinho now lies on the seabed about a kilometre south-west of the Lavajo sand bar near Armona.
The dredge was carrying 12,000 litres of gasoline but the possibility of environmental risks was dismissed by AMN, with anti-pollution barriers put in place immediately to contain possible oil spills.
Authorities have started investigations, but Olhão Mayor António Pina said it was too early to draw conclusions about the possible causes.
