A potentially toxic algae has been discovered in a West Sussex pond, the first time it has been found in the UK.

The rare form of blue-green algae was found at Boldings Brook, north of Horsham.

Called Arthrospira, it is potentially harmful to dogs and can cause sickness and rashes in humans.

The Environment Agency is carrying out an investigation as to how it ended up in the pond.

Sean Ashworth, the agency's area ecological team specialist, said: "We don't know how this algae found its way to Sussex as it usually occurs in warmer climates than those in the UK.

"However, with global warming and increasingly hotter summers, it is likely we may see more of this appearing in our waters."

Agency staff identified the rare algae after taking a sample.

It was then verified by scientific experts at the University of Durham and the Natural History Museum in London.

A small amount of the naturally-occurring algae bloomed during the recent warm weather.

Heavy rain over the weekend caused most of it to disperse but dog owners have been advised to avoid the area.

An agency spokesman said: "We think pretty much all of it has dispersed but because it can form again quite quickly we are advising people to stay away.

"It can be dangerous for dogs and several have died in the past so we are especially warning dog walkers."

Blue-green algal blooms are common in warm weather especially in nutrient-rich bodies of water such as ponds.

Although not all species are harmful, the agency adopts a precautionary approach and considers all to be potentially toxic.

If blue-green algae is found, all contact with the water, such as swallowing it or swimming in it, should be avoided.

Richard Morris, a spokesman for Horsham District Council, said it was unclear which local authority was responsible for Boldings Brook.

He said: "The Environment Agency said the algae was not toxic, had not bloomed and the property was away from any public access.

"The agency said the local authority responsible did not have to take action. The landowner has been notified."

The Environment Agency produces a leaflet on blue-green algae. To obtain a copy, call 0845 9333111.