David Moore, 29, of Southsea, Hampshire, was beneath the Upper Lode lock gate, near Tewkesbury, Gloucestershire, when he became caught under the water in October 2004.

He was taken to Cheltenham General Hospital, but died soon after.

The Crown Prosecution Service decided no criminal charges were justified.

A jury was sworn in this morning to hear eight days of evidence at the Manor By The Lake Hotel in Cheltenham.

Gloucestershire Coroner Alan Crickmore told the jury that Mr Moore was part of a maintenance team draining the lock, leaving the walls and floor exposed.

Temporary dams - known as shrouding - were to be installed both upstream and downstream, allowing water inside to be pumped out, Mr Crickmore explained.

Mr Moore, of Victoria Grove, was part of a three-man service team, and died in the water.

The jurors were told they would be taken to the scene to see the dimensions of the lock and the "lie of the land". They will be given life jackets and hard hats.

Gloucestershire Police, the Health and Safety Executive and British Waterways are all represented in the case.

Mr Moore's father, Alick, 66, a retired naval officer, his mother, Penny, 59, of Trudoxhill, Frome, Somerset, and his fiancee, Shelly Blane, 34, are all attending the inquest.

The inquest continues.