ALARM bells rang around Kings Pond last Thursday when the water turned a brilliant shade of emerald green.

The Environment Agency received numerous calls from worried residents concerned that whatever was causing the colour to change could kill off the burgeoning wildlife, not least cygnets, goslings, ducklings, herons, fish, and the weed and aquatic wildlife on which they feed.

But the colour change was found to have been caused by Thames Water, which had been carrying out investigative work to try to track the route of a drainage course further upstream.

To do so, they use Flourescein, a non-toxic flourescent dye that turns bright emerald in the water but will not harm wildlife.

The dye had obviously found its way into the River Wey and ended up in Kings Pond where swans made a striking contrast as they and their cygnets swam, apparently unconcerned, through the vibrant green water.

A Thames Water spokesman said: “We’re sorry if the green colour in the pond caused alarm. We can confirm it is a harmless, non-toxic dye we put down drains to trace where pipes lead to. It will have had no effect on the pond and its wildlife.”