GREATER Melbourne's green wedges are at high risk of destruction from an ever-growing population, says the National Trust of Australia.

The trust has released a report placing the green wedges in the top 10 heritage places at risk, alongside national icons such as Lake Burley Griffin and foreshore in Canberra, Macquarie House in Hobart, unprotected historic buildings in central Melbourne and the Lower Lakes and Coorong in South Australia.

First identified by the Hamer Liberal government in the 1970s, green wedges have been dubbed Melbourne's lungs. The state's Department of Planning and Community Development says they safeguard agricultural uses and preserve rural and scenic landscapes, non-renewable resources and natural areas including water catchments.

They play an important part in Melbourne's open space network, provide opportunities for tourism and recreation, and have high environmental, landscape, built or Koori heritage values.

Melbourne has 12 green wedge areas stretching from Werribee in the north-west across to the Yarra Valley, Dandenong Ranges and down to the south-east and Mornington Peninsula.

Chief executive of the National Trust's Victoria branch Martin Purslow says green wedges in outer suburbs are "an irresistible attraction to developers, who see in them the opportunity to make large profits".

He says the Government's plan to have five million people in Melbourne puts "increased pressure to replace treasured green fields with low-density housing".

Australian Council of National Trusts chairman Graeme Blackman says the National Trust is also worried about the loss of urban heritage in Melbourne and Sydney.

"Many of the buildings in Melbourne's CBD are being threatened by development and population pressures."

In addition to the 10 heritage places at risk, the Murray-Darling Basin was named as the greatest region at risk for the third consecutive year.

For more information on the 2009 Our Heritage at Risk lists, visit www.heritageatrisk.org.au