Carcasses and body parts from shot animals that will be left in the bush once hunting begins in March will provide a previously unavailable food source, according to a leaked draft risk assessment from the Office of Environment and Heritage.

''Where hunting is concentrated in specific areas, involves leaving substantial portions of carcasses behind and occurs with high regularity, it has the potential to provide a supplementary food source to local predators,'' the assessment said.

''This particularly applies to foxes but may also include cats, wild dogs and pigs.

''This may have the impact of increasing the populations of these species and increasing the impact they have on native animals and the wider environment.''

The warning will feed concern among environmental groups, bushwalking clubs and national parks associations about opening 79 national parks to feral animal shooting by amateur hunters.

Animals targeted for hunting will include deer, pigs, goats, rabbits and dogs.

Fairfax revealed on Sunday the O'Farrell government had been warned by Environment and Heritage of a ''major risk'' to the public when recreational shooting begins in March.

The office found the risk of death or serious injury was ''high'' as well as the potential for the 34 million annual visitors to decline due to concern at safety in parks from bullets and also from arrows shot by bow hunters.

Carcass dumping was likely to ''cause an offensive odour for other campers as well as increase flies, vermin and scavenging animals around camp grounds''.

''Carcasses also have the potential to contaminate streams and water bodies if left in close proximity to them,'' the assessment found. ''In addition, visible carcasses in camping or day use areas are likely to cause anxiety or some offence to some other park users.''

The assessment, which took views of hunters, the Game Council, parks staff and environmental groups, said it had been agreed hunters would not bring carcasses or other body parts within 500 metres of a campsite or day use area - ''unless the carcass or body part/s remains covered''.

Carol Booth, a policy officer with the Invasive Species Council, an environmental group focused on the threat of invasive species, said she agreed carcasses could provide extra food supply to feral animals.

Dr Booth said professional control programs killed large numbers of animals at the one time, meaning their carcass meat was available only for a short period.

A spokesman for Robyn Parker, the Environment Minister, said the risk assessment process was unfinished.

Asked whether extra animal carcasses could provide more food and lead to more feral animals, a spokeswoman for the Office of Environment and Heritage said: ''We are developing guidelines to address those issues as part of the risk assessment process.''

A spokesman for the Game Council of NSW, Greg McFarland, said licensed hunters would treat carcasses in accordance with the office's requirements.