Getting to the bottom of river's smell

POLLUTION is not the cause of a foul smelling grey river in Bury St Edmunds, experts have concluded.

Naomi Cassidy

POLLUTION is not the cause of a foul smelling grey river in Bury St Edmunds, experts have concluded.

The Environment Agency (EA) began investigating the situation on the River Lark at Eastgate Street after members of the public reported bad odours and claimed that the river had turned a milky grey colour.

Following an investigation, officers ruled out pollution after taking water samples for testing. It appears the changes in the river have actually been caused by a natural process, brought on partly by climate change.


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The EA has since pumped hydrogen peroxide into the river to supplement the oxygen content of the water, resulting in a reduction of the smell, preventing further deterioration, and reducing the risk of harm to fish.

Nick Dyer, from the EA, said: “All the symptoms were consistent with an anaerobic environment on the river bed. This is a natural phenomenon which occurs when oxygen levels are very low.”

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He explained that the lack of oxygen causes the river bed to become anaerobic (without oxygen), which results in the sulphurous odour similar to the smell of bad eggs that has been reported by passers-by. The gases also give buoyancy to the organic matter on the bed, which causes it to float to the surface and cover the watercourse.

Mr Dyer added that the phenomenon has led to the deaths of many of the insects on the river bed although the fish have managed to avoid this fate.

He added: “It is widely recognised that climate change is a significant contributing factor to such occurrences. Should weather patterns continue to follow projected trends incidents like this will increase.

“The total lack of oxygen along a several 100 metre stretch of river has resulted in the deaths of the majority of insects that live on the river bed but fish have been able to swim away from this section. However, heavy rainfall which is likely after a prolonged dry period, is likely to result in deoxygenated water being pushed down river resulting in a risk to fish caught in it.”

The hydrogen peroxide added to the water is a temporary solution to help the situation until nature takes its course and the rate of flow of the river is increased.

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