Emergency crews worked into the night on Wednesday to remove the bodies of two workmen from a partially-submerged fuel tank at Oulton Broad, near Lowestoft in Suffolk.
Rescue workers said that the men had been in the tank since about 1400 GMT and crews were not optimistic about their condition when they arrived on the scene later in the afternoon.
Ed Meelan with the Suffolk Fire Service said crews had been concentrating their efforts on extricating the men from the tank, which is 5 metres wide and 15 metres deep.
They were not identified.
The tank, one of several on the water in an industrial area in Oulton Broad, is believed to be empty.
The Health and Safety Executive has launched an investigation into the incident.