Search: Cyanide sewage River Trent
Levels of cyanide and untreated sewage in one of the country's major rivers are falling as experts continue their investigation into how the water became polluted.
Environment Agency officers were out overnight pumping oxygen into the River Trent in Staffordshire after the "serious pollution incident", which has already killed thousands of fish.
The agency said it had not received reports of any humans or domestic pets being affected by the contaminated water, but would seek to prosecute following an investigation that is under way.
Reissuing a warning for people and animals to keep out of the river between Stoke-on-Trent and Yoxall, a spokeswoman said: "We have had environment officers out all night and today pumping oxygen into the River Trent, which has been polluted with cyanide between Stoke-on-Trent and Yoxall.
"Samples taken throughout the night show pollution levels have already dropped. We expect further dilution today as the Trent meets the River Tame.
"We are still asking boaters, anglers, farmers and dog-walkers to stay away from the affected stretch of river as a precaution."
The spokeswoman said the contamination was being treated as a "serious pollution incident" and could lead to prosecution.
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She added: "It is very important we know where these substances came from so we are focused on that."
No precise timeframe has been put forward but the Environment Agency said it hoped for a "swift resolution" and was monitoring the contamination as it moved downstream.
Officers are working with the Drinking Water Inspectorate and the Food Standards Agency and members of the public have been urged not to extract water from the river.
