Fishermen are awaiting the results of tests to see if they will be allowed to resume catching shrimps from The Wash. Results are not expected until tomorrow.

Water quality has almost returned to normal in the centre of Peterborough with no new fish deaths reported, the Environment Agency said this afternoon.

But the Food Standard Agency, which has banned the gathering of shellfish and shrimps, said it was still awaiting the results of tests to see if fishing could resume in The Wash.

Fishing was suspended after thousands of coarse fish died in the aftermath of the spillage at Orton Southgate.

The Food Standards Agency feared that the chemical - which has not been named - could have found its way downstream into The Wash via the Nene Outfall, at Sutton Bridge.

But this afternoon, a spokesman for the Environment Agency said: 'We are no longer seeing fish struggling in the water and believe the worst to have passed but we are staying alert and continuing to monitor throughout the week and weekend.'

Tens of thousands of fish were seen in distress along the length of river from Orton Mere to Wisbech after the 5,000 litre chemical spill at the weekend.

Earlier today, the Food Standards Agency said it had banned the gathering of fish and shellfish from the River Nene and The Wash as a 'precautionary measure'.

'The Food Standards Agency is expecting results today from samples that have been taken by the Environment Agency and local authorities in the potentially contaminated areas,' a spokesman said.

'Once we have these results we will contact the relevant local authorities and provide further advice on this situation.'

Fishermen in King's Lynn, the largest port affected by the stoppage, said it came three days after the start of the cockle season.

Around 50 tonnes of shellfish landed yesterday are believed to have been impounded.

West Norfolk council's environmental health officers are carrying out tests on shellfish as a precaution.

Police and Environment Agency officers are still investigating the cause of the chemical spill, which happeened over the weekend.

While an estimated 5,000 litres found their way into the river, much of the spillage was contained by closing a sluice gate. Scientists said rain would have diluted the substance before it found its way into the tidal river, at Dog in Doublet, near Whittlesey.

The EA said species affected were mostly small roach, with some tench and eels also dying. Steep banks prevented fisheries staff from attempting to rescue thousands more fish seen in distress.

Anglers have also been asked to avoid fishing the river to allow fish to recover. The ban comes days after the start of the river fishing season.