No, you’re not seeing things, this river really is luminous green.

United Utilities engineers put harmless dye into a two kilometre stretch of Colne Water, at Trawden to help them pinpoint where river water was finding its way into the local sewer system.

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Following the December floods, excess river water had washed away a section of banking and found its way into the sewer.

The extra volume of water entering the pipe, while not causing a pollution problem, has placed the sewer under strain.

Network engineer Matt Atherton said: “The dye allowed us to see where the river water was finding its way into the pipe.

"It was simply a case of peering down various manholes along the length of the sewer, until we saw green!

“We’ve now found the section of sewer we need to work on. The next step is to pull together a repair plan.”

The dye naturally dissipates after a few hours, and does not harm aquatic life. United Utilities engineers have various colours of dye at their disposal, but green is often favoured for jobs of this kind.