Pollution is believed to have killed hundreds of fish spotted floating along the River Stour in Ashford.
The Environment Agency is now investigating the cause for the deaths but said that initial findings suggest the problem has been contained to the Ashford area.
Ruth Moore, 66, of Tufton Road, Ashford, and her daughter Hannah Moore, 38, reported the dead fish to the Environment Agency yesterday afternoon after they saw them on their walk home near the Stour Centre.
Mrs Moore said: “It was a sad and horrible sight. We are an animal loving family and the worst part was seeing the big pike dying and struggling for air.”
"it was a sad and horrible sight. we are an animal loving family and the worst part was seeing the big pike dying and struggling for air" – ruth moore
Lewis Brown from the Environment Agency said: “The Environment Agency was made aware of a pollution incident on the River Stour in Ashford yesterday afternoon.
“Our officers attended the scene and have been working with Kent County Council and Ashford Borough Council to investigate. We are monitoring the situation.
“Our initial investigation suggests that the impact has been localised, this morning we have not seen any fresh signs of pollution or fish in distress."
The Environment Agency is appealing to anyone with information about the pollution to call their hotline.
Mr Brown added: “If anyone has seen anyone acting suspiciously or has concern or information about pollution to the river please call our emergency hotline 0800 807060.”
It is not believed to be related to deaths of frogs in Singleton Lakes in Ashford.