On Monday people enjoying Singleton Park spotted a strange sight: the stream running through it had turned bright green, and we've now been able to discover the cause

Local Swansea resident, 23-year-old Tom Judge, noticed the fluorescent water while running with his girlfriend in the park at around 5pm.

He said: "It was bright florescent green and didn't look natural at all. We were both really shocked."

The following day the water returned to its usual state and Natural Resources Wales (NRW) launched an investigation into what had caused the colour change.

That investigation has now concluded that the green water was caused by dye.

The investigation has concluded
It was brighter at one end of the park

A "dye tracing drainage survey" was carried out, which means brightly coloured dye was added to the stream in one place to see where the dye ended up.

The method is often used by urban planners and developers and the dye used is harmless.

This particular stream runs under Swansea for almost a mile and is part of an urban underground waterway that flows under the city. 

Sarah Bennett, environment officer for NRW, said: “Many years ago the watercourse would have been an open natural stream. Where possible NRW would encourage urban planners and developers to open up these culverted watercourses and restore the streams to as natural a state as possible.

“May we remind anyone carrying out such tests to inform us at NRW. This will help us respond to reports that the water has changed colour and it means we can contact them to let them know where their dye has appeared."

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She added: “They should also minimise the amount of dye used, and make sure that any misconnected foul drains they discover are reported and rectified. You can find out more about drains and misconnections by visiting http://www.connectright.org.uk/.” 

Call 0300 065 3000 for any further advice on dye tracing.