Why does the River Calder turn orange?

Witnesses have described the River Calder in West Yorkshire as resembling "tomato soup" after it turned a bright orange colour.

Pictures and videos posted on social media showed the river flowing a vibrant colour on Thursday, 24 October, with some describing its appearance as "insane".

It is not the first time water courses in the area have been discoloured.

Similar events occurred in both 2014 and 2022.

The Environment Agency said it had sent officers to investigate the source of the issue.

Why does the river turn orange?

Despite tongue-in-cheek speculation that there had been a serious tomato soup leak, or that thousands of litres of Iron Bru had somehow found their way into the river, the explanation is much more mundane.

A number of social media users were quick to point out the correct reason, identifying disused mines as the source.

In a Facebook post, Elaine Horsted wrote: "It’s iron from the hill water... It’s always happened when we’ve had a lot of hill water from the old mines up there."

Dave Halley added: "Last time it went down the road and dyed all the roadside house's orange to about 4ft for a couple of miles."

The Environment Agency confirmed as much, in a post on X.

A spokesperson said: "We've received reports about the River Calder turning bright orange in Todmorden, which is due to water escaping from old mines.

"Officers are investigating the source, but we don't expect any significant or long-term water quality issues."

The agency is not expected to take any further action, with the colour returning to normal in due course.

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