A briefing document produced by the Premier's department has laid bare the lethal threat posed to the public when recreational shooting of feral animals begins in March.

It also warns of reduced visitor numbers to national parks ''because people don't like the idea of shooting'', and damage to the National Parks and Wildlife Service brand.

Waterways, especially those in areas that supply drinking water, will be threatened by rotting animal carcasses and there will be increased risk of diseases and weeds being introduced to the 79 NSW parks due to be opened to guns. The report also raises the need for parks staff to wear high-visibility clothing to avoid being accidentally shot by hunters.

In New Zealand, where hunting is allowed in national parks, a school teacher, Rosemary Ives, was shot dead at a camp site in 2010 after a hunter ''mistook her for a deer''.

The Draft Risk Assessment, produced by the Office of Environment and Heritage and dated December 10, 2012, lists groups at risk from ''projectiles causing death and serious injury to people'' as parks workers and visitors, including ''families, special user groups, remote visitors''. Hunters, whether shooting by permit or illegally, are also at risk, as well as ''neighbours'' with properties that border the 2 million hectares of parkland to be opened to hunters.

The 59-page document said the risks to these groups was ''major and the likelihood as possible … giving a risk rating of high''.

Sections of Environment and Heritage - which answers to Environment Minister Robyn Parker but operates inside the Department of Premier and Cabinet - are understood to be fiercely opposed to hunting.

The risk assessment was leaked to the Labor opposition and the Greens last week and passed to Fairfax Media on Friday. It has emerged just days before the December 27 deadline when changes to the Feral Animal Control Act become law.

Mr O'Farrell personally negotiated a deal in May that resulted in the Shooters and Fishers Party supporting the government's $3 billion electricity generator privatisation in return for access to national parks for amateur hunters.

Bushwalkers, representatives of parks staff, environmental groups and opposition parties called for a rethink from the government. Opposition environment spokesman Luke Foley said: ''If something goes wrong in one of the national parks, Barry O'Farrell will not be able to say he was not warned. For the government to proceed after receiving this warning, it would be abandoning its duty to community safety.''

Mr O'Farrell's office declined to comment but a spokesman for Ms Parker said a risk assessment was ''good operational practice''. ''Workshops with NPWS staff and experts in pest management, safety, environmental protection and risk management are identifying the possible risks to be managed and the appropriate controls.

''The risk assessment will allow the NPWS to tailor strict controls to suit circumstances in each park.'' The draft risk assessment predicts confrontations between the public and hunters and parks officers and hunters as ''high to medium''.

Representatives of the state's biggest 54 bushwalking clubs said confrontation was inevitable. Keith Muir, director of the Colong Wilderness Foundation for protecting national parks, said some bushwalkers will be incensed their freedom has been taken, while others will be put off by the perceived dangers.

''They will be discouraged by this. It's very sad because we're supposed to be encouraging people to get outside and exercise and to get visitors into our national parks,'' he said.

Under the heading ''post-incident controls'', the risk assessment calls for clear emergency procedures in the event that someone is shot, including training for first responders and first aid.

In terms of high-visibility clothing for hunters and parks workers, it said: ''This may reduce the probability of failing to see people who are inconspicuous against the natural landscape. This is particularly in a context where some park users deliberately use inconspicuous clothing to reduce their visibility and disturbance to wildlife.''

Steve Turner, of the Public Services Association, representing rangers and parks workers, said national parks would become ''Mickey Mouse playgrounds'' if his members were forced into fluorescent gear.

Sydney Morning Herald