The Environment Agency is carrying out an investigation after fish were killed in a pollution incident at Willow Brook near Corby.
A member of the public reported the incident on Saturday (June 21).
An environment Agency spokesman said: “We were contacted by a member of the public on Saturday about a pollution incident at Willow Brook. We sent out environment and fisheries officers to assess the situation, who found that there was a serious incident with fish killed.
“The discharge stopped on Saturday afternoon and the circumstances around it are being investigated. We will be sending further teams out this week to assess the full environmental impact of the incident.”