Following a three month investigation the Environment Agency has failed to identify the cause of the pollution that destroyed the whole of the fish life of the Welsh Dee.

A spokesperson said that the investigation was ongoing but that the Agency might never solve the mystery of how more than 100,000 fish lost their lives along the river between Bangor-on-Dee and Chester.

It is estimated that it could take 10 years for the fish stocks in the river to return to normal following one of the worst cases of pollution ever to hit north Wales.

The spokesperson added, “A lot of money has gone into this investigation – we want to find out as much as we can and exhaust all possible avenues.”

One theory is that the pollution was a natural disaster. It is said that stormy weather at the time of the pollution last July robbed the fish of oxygen when floodwater disturbed mud and silt on the riverbed.

Environment Agency Wales managers met representatives of River Dee angling clubs and other interests at Buckley on (Tuesday to give them an update on investigations into the major fish kill incident.

David Gatehouse, Environment Agency Wales Northern Area Manager, said: “Whilst we do not know what caused the incident, we know a plug of de-oxygenated water moved downstream from just below Bangor-on-Dee to Chester Weir over a period of 50 hours. We are still considering a number of possible causes and our investigations are continuing.”

Alan Winstone, Northern Area Fisheries, Ecology and Recreation Manager said: “Already 20,000 small roach have been restocked into Aldford Brook, and a further 1,000 large chub and 800 large barbel will be stocked later in the year from the Agency’s Calverton fish farm at a cost of £ 3,000. Angling representatives have agreed to work with us in partnership to secure funding and help deliver the plan.”