The Environment Agency believes an accidental spillage of sugar could have caused last year's pollution alert on the River Dee, when 100,000 fish were killed.

The incident last July was one of the worst on record and agency officials have warned that a prosecution for negligence is still a possibility.

Pollution investigators carried out a full report into the incident and they believe they may have found the cause.

The investigation team was baffled when no traces of chemical pollution were discovered in the Dee, and the EA inquiry focused on what might have caused oxygen to have been stripped from the water.

Now it is thought that spilt sugar may have been eaten by bacteria found in legally dumped sewage.

Accidental

As the bacteria broke the sugar down into water and carbon dioxide, oxygen was removed.

This led to a plug of deoxygenised water passing down river, killing the fish.

As sugar is a valuable commodity, the assumption is that the sugar spillage was accidental.

But, if enough evidence can be gathered in the next few months, a prosecution for negligence has not been ruled out.

Years to recover

The agency initially estimated that 10,000 might have been killed.

Officials believe it will take years for fish stocks to recover from the disaster.

At the time of the incident, the agency investigated agricultural and commercial buildings along the river to see if any chemicals or waste may have escaped or been dumped.

The general public was also called on to help solve how the fish had died.

The River Dee was struck by a major pollution incident several years ago.

Since then the river has been the subject of close monitoring.