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.
- Send your Letter to the Editor: What do you think? We welcome letters from our readers on a wide variety of subjects and you can send us a letter for publication here
Our top stories
- UPDATE: Three more men arrested in connection with attempted murder after altercation in Banbury
- Oxford United v Swindon Town - UPDATES
- CLARIFICATION: Hygiene report of Delight 2 in Didcot
- Man 'obsessed' with BBC journalist goes on trial after allegedly breaching restraining order against her
- Families urged to consider signing up for organ donation
- Oxford United send match tickets to fans caught up in season ticket delay