The Environment Agency has launched an investigation to try and uncover why “hundreds” of fish died in a tributary of the River Tyne in Northumberland.

Staff from the Environment Agency (EA) were on the scene at Park Burn at Prudhoe Riverside on Wednesday and Thursday testing the water after walkers spotted the dead fish and reported the issue. Northumbrian Water has also tested the water in the burn and said the pollution did not come from any of its sites.

However, technical advisers for the company did attend on Wednesday and noticed “discolouration” of river water from a “culverted water source” not belonging to the water board. This has been reported to the Environment Agency for “further investigation”.

Park Burn flows into the Tyne after passing the chalk heaps known as the Spetchells, via the Low Prudhoe Industrial Estate. In a statement, the EA thanked the public for reporting the incident.

A spokesman for the agency said: “Our teams are on site to investigate a pollution to Park Burn in Prudhoe. We would like to thank the members of the public that have reported this incident to us.

“Members of the public can report environmental incidents 24/7 365 days of the year to our incident hotline on 0800 80 70 60. It is crucial that we receive timely reports with as much information as possible to help us undertake investigations.”

The EA did not comment further as to not prejudice the ongoing investigation.

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Northumbrian Water said it had checked its wastewater network in the area and were “confident” that the issue was not related to any of its operations. The company is assisting the EA in the investigation and sent water samples for analysis.

Coun Gordon Stewart, who represents the Prudhoe South ward and is cabinet member for communities, described the reports as “distressing”.

Coun Stewart said: “I’m very much aware of the issues at the riverside which is distressing to hear about. I’m awaiting the outcome of the Environment Agency’s investigation.”