The public is being asked to keep a look out for the 'pink peril' spreading through the Broads.

The plant Himalayan Balsam was introduced to Britain in the 19th century but it is only in the last year or two that it has begun to spread rapidly through Broads fenland.

It had been thought that the plant, native to the Himalayas, was mainly confined to riverbanks, but aerial pictures commissioned by the RSPB show its alarming march.

The Broads Authority's senior ecologist, Andrea Kelly, said: 'In tall fens it is very hard to see what is going on.

'This picture shows quite substantial areas of fen have been taken over by Himalayan Balsam.'

The picture by Mike Page shows the plant spreading around Surlingham Broad, but Ms Kelly said it had taken over many other areas, including land around Brundall, the River Ant and River Bure.

The danger is that Himalayan Balsam can smother native plants and affect the ecological balance.

For example, milk parsley – one plant that could be hit – is the food source for the swallowtail butterfly caterpillar.

The public is urged to keep a look out for Himalayan Balsam and log findings on the website www.nbis.org.uk/BroadSweep2011

Ms Kelly said: 'All the conservation organisations will get together over the winter to sort out a plan and funding to hit the plant hard.'

Volunteers could become involved next year in parties that would go out and physically remove it.