Probe after 1,500 fish die in Picknall Brook, Uttoxeter
More than 1,500 fish have been found dead in a polluted brook in Staffordshire, prompting an investigation.
The Environment Agency said the pollution in Picknall Brook, Uttoxeter, came from an "agricultural source".
The water flows into the River Dove but the group said there had been "no visible impact" on the river's ecology.
It said it was still considering its enforcement response and was looking at plans to stop it happening again.
Environment Agency spokesman Susan Bowen said: "Our initial assessment is that over 1,500 fish have died in the brook, mainly bullheads and minnows, although we are still assessing the impact.
"The pollution has now passed and dissipated, so we can confirm that water quality in the brook has returned to normal, and we will look at ways we can help the brook's ecology to recover.
"Because of the on-going investigation and the fact we are still considering our enforcement response, we are unable to give any further information at this stage."
Staffordshire County Councillor for Uttoxeter, David Brookes, said it was "an unfortunate incident".
"I understand the pollution has now gone but I would suggest livestock are kept away from the brook for the time being," he said.