Police have launched an investigation into what caused a pollution leak that killed thousands North Yorkshire fish last week.

The farm at the centre of the slurry leak said that vandals are responsible - and last night Durham Police confirmed an inquiry has been started.

Thousands of fish died after digestate material from AWSM Farming, in Hutton Magna, drained into a nearby river, causing watercourses across Richmondshire to “run black for hours on end”.

The Environment Agency confirmed that they were “assessing and mitigating” the impacts of this incident, though local businesses dependent on the impacted waterways have said that it is a “huge financial hit” and “takes the area hundreds of steps back ecologically”.

Read more: Fears of pollution as fish dead in Richmond and Northallerton rivers 

Previously, the farm has been subject to large fines for environmental hazards that included pollutants leaking from storage containers, and mistakenly using a carcinogenic as a fertilizer.

In 2017, ASWM Recycling was hit with hefty fines for environmental hazards that killed fish and other aquatic animals.

In two cases, pollutants leaked from storage tanks owned by the company. On one occasion, the company mistakenly used a carcinogenic as a fertiliser, and spread banned burned blood waste across farmland in Stillington, near Stockton. Too much blood waste was used, and it leaked into a nearby beck.

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Adam Metcalfe, of Lane Head Farm, Hutton Magna, in Teesdale, was fined a total of £1,000 and AWSM - of which he is a sole director - was fined £20,000.

Edward Bennett, AWSM’s Environmental Manager, said: “Despite having robust controls in place, we discovered that one of our digestate stores had been vandalised on 13-04-2023, leading to the loss of digestate contained within the store. 

"This was promptly reported by us, to the Environment Agency and the police on the morning of the event. 

“We have been working very hard to clean up and mitigate the impact of the digestate, while working closely with the Environment Agency and police to assist them with their ongoing investigations.”

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Durham Police said: "We received reports of criminal damage at an address in Hutton Magna on Thursday (April 13).

"It is believed the suspects caused damaged to a tank lock causing a quantity of slurry to go into a nearby river.

"Enquiries are now ongoing however officers are keen to speak to anyone in the area at the time."

An Environment Agency spokesperson said: “Our officers attended a pollution incident last week spanning a number of watercourses near Richmond, North Yorkshire to assess ecological impacts and mitigate any harm to the environment. The discharge has now been stopped and the water is running clear.

“Ecologists have taken samples to evaluate the impact to wildlife and we are awaiting lab results to understand the full extent and impact of the incident.

“Members of the public can report environmental incidents to our 24/7 incident hotline on 0800 807060.”