A RIVER turned bright blue when an unknown substance polluted the water earlier this month. The blue water was seen flowing along the River Red in Redbourn on the morning of October 4 but it reverted back to its normal colour within a few hours. Mandy Jam

A RIVER turned bright blue when an unknown substance polluted the water earlier this month.

The blue water was seen flowing along the River Red in Redbourn on the morning of October 4 but it reverted back to its normal colour within a few hours.

Mandy James at Redbournbury Mill was the first to notice the unusual phenomenon.

She said: "I got up in the morning and the river was an opaque, fairly bright-blue colour. It did give me a shock as it was so blue."

Mandy called the Environment Agency's emergency hotline and investigators were soon on the scene but they immediately established that there was no threat to wildlife.

John Fisher, of the Ver Valley Society, visited the river a couple of hours afterwards to find it had become a dull grey/blue colour. He has never known any rivers in the area to change colour before.

A spokesperson for the Environment Agency said: "Our officers visited the site and found no odour or distress to wildlife. We have not yet found a source of the pollution but we believe it may have originated from a surface water balancing pond in Hemel Hempstead. We are currently investigating this.