A river running through Wimbledon Common has attracted a bit of attention after turning green out of the blue.

The Beverley Brook is a nearly nine mile stretch of water that covers a large portion of south-west London.

But as of this week, parts of the water, including that which enters Wimbledon Common, changed colour.

"Following reports from concerned members of the public about a green substance in the Beverley Brook where it enters Wimbledon Common near the Wimbledon Rugby Club playing fields, WPCC have been in contact with the Environment Agency," the Wimbledon and Putney Commons Conservators said.

"They have advised that it is a fluorescent dye and although they and Thames Water are investigating the matter they have assured us that it is not toxic and is diluting as it flows down the Brook."

People were also voicing their confusion on Twitter, with Thames Water replying directly to some as well, although no answers are clear.

"I've spoken to our team and we've been out to investigate," the water company replied to one concerned person.

"As it's such a wide spread area, we're having to take a bit more time to figure out what's happened. But we'll get this resolved as soon as we can."

A spokesman for the Environment Agency said: "We are investigating the discolouration of the river, which we believe is caused by dye used for tracing drainage systems.

"This type of dye is harmless to the aquatic environment."