The number of dead fish in a stream has risen to 4,400.
The gudgeon, chub, dace, roach and other species have been found by the Environment Agency (EA) in Moor Ditch north of the Ladygrove estate since Saturday.
The EA said water samples indicate the presence of a detergent or cleaning product but it is still investigating the source.
A spokesman said there had been a “dramatic” improvement in the water quality since it was first called in.
He said: “Efforts continue to trace the source of the pollutant but we believe the discharge has stopped. Water quality is now returning to normal and live fish have been seen at various points in the Moor Ditch.”
Anyone with information about the incident should call the EA on 0800 807 060.
- Do you want alerts delivered straight to your phone via our WhatsApp service? Text NEWS or SPORT or NEWS AND SPORT, depending on which services you want, and your full name to 07767 417704. Save our number into your phone's contacts as Oxford Mail WhatsApp and ensure you have WhatsApp installed.
Our top stories
11:20am Monday 28th July 2014
What do you think? We welcome letters from our readers on a wide variety of subjects and you can send us a letter through the blue headline above.
7:30pm Friday 12th February 2016
THE next time Kemar Roofe shouts “on me head” to a teammate, he will be hoping it’s a football rather than a custard pie.
12:00pm Thursday 11th February 2016
AN INSPIRATIONAL teenager who laughed his way through life has died after doctors met his wish by switching off the machine keeping him alive.
7:00am Thursday 11th February 2016
A NEW free school with a Christian ethos could open in Headington to help relieve pressure on existing schools.
7:30am Wednesday 10th February 2016
SUNKEN boat owner John Simmonds was stunned into silence yesterday when he was handed hundreds of pounds worth of donations from Oxford Mail readers.
6:30am Wednesday 10th February 2016
In a special report, the Oxford Mail exclusively reveals how the owners of Oxford Stadium were still making a profit before closure despite claims it wasn't "viable"
8:00am Wednesday 10th February 2016
FANS could soon be buying Oxford United toothpicks, pet clothing and even lingerie after the club registered its name as a trademark.