The National Rivers Authority is investigating the contamination, which may have been caused by illegal fly- tipping into a sewage system near Nottingham.
Of about 500 anglers who took part in a National Fishing Union match on Saturday, those below the Stoke Bardolph sewage works outfall, near Nottingham, caught nothing, while those above it achieved catches of 10lb or more.
'Something was drastically wrong with that river,' one competitor, Tony Warburton, a member of the Clean Rivers Trust, said.
Yesterday, dead fish were picked out of the river at Newark, 18 miles downstream.
An NRA spokesman said: 'We are still counting dead fish and trying to find the cause. It looks as if it was a fairly significant contamination.'
A spokesman for the Severn- Trent water company said: 'We believe there may have been an illegal discharge of a substance which adversely affected the biological process of our Stoke Bardolph sewage treatment works. The substance may well have passed through and had an impact on the river Trent.'
Harvey Wood, a Clean Rivers Trust co-ordinator, said: 'It could take years for fish stocks to recover.'Reuse content