You are in [Events] [1998 Hungerford Fish Mortality]
In the early hours of 4 Mar 1998 the Berkshire Trout Farm (at Dun Mill, one mile east of Hungerford) reported tens of thousands of dead and dying fish. This catastrophic event was reported on the news media world-wide.
By dawn it was apparent that the incident had originated in the Kennet & Avon Canal near Froxfield (west of Hungerford). Wild fish populations in both a 4km stretch of the canal and in the River Dun up to Freeman's Marsh had suffered the same fate. No fish were dying downstream of the Trout Farm, and no other wildlife was affected.
Initial tests for chemical contamination (cyanide, agricultural pesticides) were clear, and dissolved oxygen levels and ammonia were also normal.
Post-mortem examination of the fish showed severe damage to their gills - the worst ever seen by the fish pathologist. The fish had suffocated despite there being plenty of oxygen in the water.
Whilst ongoing investigation was carried out, it was necessary to clear the area of dead fish, lest this contamination would have threatened the rivers downstream. The clear-up operation was to take five weeks - 150 tonnes of fish, filling 30 skips.
The canal was closed to traffic.
Over the following few weeks it became apparent that there were surges of toxicity in the same stretches of canal, resulting in further fish deaths. This fluctuation in toxicity does not happen where a pollutant has entered water courses either accidentally or deliberately.
Over 200 water samples were compared against almost 275,000 known man-made chemicals. These tests ruled out man-made chemicals, including herbicides, pesticides, radioactive isotopes, heavy metals, nitrates, solvents, detergents, oils and narcotics.
The Environment Agency focussed on natural sources. Algal toxins had already been excluded, but evidence pointed to a toxin produced by bacteria living in the water.
The preceding month (February 1998) had been one of the mildest on record, with only 10% of the monthly average rainfall.
It seemed that the toxin had triggered a natural defence response in the fish, causing their gills to grow extra tissue as protection. However, the toxicity was so great and the tissue growth so excessive, that it very quickly reduced the ability of the fish to breathe, leading ultimately to their death.
Laboratory tests showed that the bacterial toxin could be broken down by treating the water with hydrogen peroxide. On Saturday 28th March Environment Agency staff began dosing the affected parts of the canal with peroxide. Subsequent tests confirmed this action had been successful, and the water was no longer harmful to fish.
The canal was re-opened on 3 Apr 1998.
Since then changes have been made to the flow of the river at The Orchard, on Freeman's Marsh, to prevent canal water flowing into the river.
The local fishing rapidly returned to the top quality fishing it had previously enjoyed - both in the canal (Hungerford Canal Angling Association), and the fine chalk-stream trout fishing on the Town and Manor waters of the Rivers Kennet and Dun.
The Environment Agency continues to monitor water quality locally to prevent a recurrence of this dreadful event.