Thousands of fish have died in an important salmon spawning headwater as a result of anaerobic digestate entering in the River Mole in north Devon, according to the Environment Agency (EA), which said it was the region's "largest ever fish kill".
The agency said yesterday that it had completed its initial assessment into the incident and identified the source and pollutant but that it was continuing to investigate.
More than 5km of the river was affected and approximately 10,000 fish died, according to the agency, but the chief executive of the Rivers Trust Arlin Rickard said it is likely that many more fish would have been affected.
Salmon numbers are declining and the Mole - a tributary of the River Taw where much restoration work has taken place - is an important headwater for one of England’s best salmon spawning grounds, according to Rickard.
“It’s one of the few successful salmon spawning grounds where young salmon survive... it is the lungs of the salmon system,” said Rickard. “The best headwaters have been damaged.. it is a terrible mess that will impact the whole river… it is really very bad indeed.”
It is not the first time digestate has been responsible for a major pollution incident. In 2017 in Plaistow, Sussex, a digestion plant repeatedly polluted a stream on farmland before going into administration. In 2012, Biogen UK Ltd pleaded guilty to polluting a stream in Bedfordshire with digestate, and in 2005, Andigestion polluted the river Tamar in Launceston, Cornwall with slurry.
“We are seeing more and more of this and take no satisfaction in saying we told you so,” Rickard told ENDS. He is “all for green energy” where the plants use by-products or waste but does not agree with taxpayer subsidies which encourage operators to grow maize as a feedstock.
Maize is a “very problematic crop”, according to Rickard, because it causes run-off which can lead to flooding and makes soil susceptible to erosion which can pollute rivers and lead to more fish kills. He wants the government to drop the subsidies and for plants to be better managed.
Meanwhile, another major fish kill has been reported on the River Sheppey in Somerset. The EA said it has carried out fisheries and ecology surveys between Dulcote and Coxley and said around 3,000 fish have been killed. “We are continuing to survey up to Godney… [and we are] working to restore dissolved oxygen levels,” it said.
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