The company was fined £3,400 and ordered to pay £1,000 costs to the Environment Agency which investigated the offence.

Officers found that dirty water from around the farm’s slurry storage tank had been getting into the ditch, which they described as being very black in colour. They advised farm manager and company director Mark Jude, that he needed to get the ditch cleaned up.

By the time they returned to the farm six days later, two dams had been put in the ditch and Mr Jude was advised to remove the water which had built up behind them.

But five months later when officers returned to do a further follow-up check, the ditch was still black and there was sewage fungus on the bed of the ditch downstream of the overflow pipe.

Sewage fungus is associated with organic discharges and is a sign of persistent organic pollution as it takes some time to develop.

In an interview Mr Jude said he had opened the valve on the sluice gate before the incident in August in order to release water from the farmyard into the ditch that had accumulated around the slurry tank after it had been raining heavily.

It was normal practice, he said and he would always smell it first to check that it was not contaminated. He had immediately blocked the ditch after the Environment Agency’s visit in August and had not realised there was a problem. Mr Jude admitted that he knew the ditch connected to the River Wissey at the end of his farm.

But officers were so concerned that the pollution would travel further along the stream affecting already low oxygen levels because of the time of year, that they put two aerators in the river for four days downstream of the discharge.

They had to contact abstractors downstream, including Anglian Water, who could potentially be affected by the pollution and the water company decided to close their abstraction from the Wissey at Stoke ferry as a precautionary measure and it remained closed for seven days.

Among the hundreds of dead fish found by Environment Agency officers were brown trout and eels and the trail was from the road bridge at Necton to a wooded area just north of South Pickenham.

It is clear from the government publication The Code of Good Agricultural Practice for the Protection of Waters (‘The Water Code’), that dirty water should never be allowed to flow into a watercourse.

JD Pigs admitted :On or about 11 August 2004 did cause poisonous, noxious or polluting matter to enter controlled waters, namely the River Wissey near Bradenham, Thetford, Norfolk, contrary to s85(1) Water Resources Act 1991.

After the hearing Environment Officer Eileen Daly said: ‘This case illustrates how important it is for farmers to manage their slurry and dirty water systems in line with the recommendations in the DEFRA Code of Good Agricultural Practice for the Protection of Water (‘The Water Code’) to avoid pollution incidents like this one.

‘Slurry and dirty yard water are highly polluting in the water environment. Although there may have been no intention to cause a pollution, the company’s poor method of slurry/dirty water management on the farm caused a serious pollution of an important watercourse, resulting in a major fish kill.

‘It is important that farmers undertake their work in away that does not damage the environment. Failure to do so may result in prosecution. The Environment Agency provides advice and guidance on how to prevent pollution and this can be obtained from our website www.environment-agency.gov.uk, any Agency office or by telephoning 08708 506506.’