River charity warns of 'incredibly sensitive' river after unexplained fish deaths

“The recent fish deaths seen on the River Calder through Normanton, Wakefield, and Mirfield are very concerning,” it said. “The locations and timing of these incidents point to a broad stress on the river from an extended warm and dry period, leading to low flows and increased water temperature.”

While many on social media have speculated that the deaths are down to acute contamination incidents such as sewage spills, the trust explains how longer term trends could be responsible for the as yet unexplained deaths.

“These fish deaths appear to be in parts of the river which have been heavily modified, with unnatural flows, and so lack the pool and riffle features which allow rivers to naturally maintain healthy oxygen levels. What these incidents highlight is that our rivers are unable to act or react naturally, and they are incredibly sensitive to the pressures around them and of climate change.”

The statement continued: “We expect these conditions (prolonged warm, dry spells punctuated by intense storms) to become more frequent and pronounced. We will continue to liaise with the Environment Agency during their investigations.”

An Environment Agency spokesperson said: "We believe that many of the problems we are seeing are as a result of low dissolved oxygen due to a combination of the high temperatures we have experienced recently, and the low atmospheric pressure caused by the thunderstorms. However, our officers are investigating at multiple locations to rule out any other causes such as pollution.

“It is important that members of the public who spot fish in distress report it so that our officers can investigate.”