Sussan Ley released detailed reasons on Tuesday for her decision to assess the proposal as a controlled action, requiring more information from the proponent on various aspects.

Her assessment found the proposal - which involves flying a helicopter from Derwent Bridge to land near Lake Malbena for a maximum of 120 return trips per year - would have "a significant impact" on wedge-tailed eagles and wilderness quality.

Despite a detailed flight plan showing that the 11-minute helicopter trip each way would fly at 1000-metre altitude where possible and biannual nest searches would be undertaken, Ms Ley was not satisfied it would "effectively address the risk of disturbance to the Tasmanian wedge-tailed eagle".

"I was satisfied that the proposed action is likely to adversely affect habitat critical to the survival of the species or disrupt the breeding cycle of a population, and therefore have a significant impact on the Tasmanian wedge-tailed eagle," she concluded.

The department received conflicting assessments from the proponent and opponents regarding the impact on wilderness values. The proponent claimed helicopter noise had a four-kilometre lateral noise footprint for two minutes maximum, but opponents believed it to be audible 16 kilometres away for at least five-and-a-half minutes.

An assessment by wilderness walking track consultant Martin Hawes - similar to Parks and Wildlife findings - indicated a reduction in wilderness quality over 7100 hectares due to "time remoteness" being affected with the presence of a helicopter.

MORE ON THE LAKE MALBENA PROPOSAL:

Ms Ley found that although the helicopter would be "temporary or transient", it would be used on an ongoing basis while the standing camp at Halls Island in Lake Malbena operated.

"I found that the anticipated loss of 700 ha of 'high quality wilderness area', and the reduction in 'wilderness quality' over at least 4200 ha, would constitute a significant impact on these key values or attributes," she wrote.

"I consider that the scale of the projected reductions in 'wilderness quality', including the size of the total area effected, mean that the impact on relevant values is substantial.

"Having considered the advice in the recommendation brief and the attached material, I found that the impact on the world heritage values of the Tasmanian Wilderness World Heritage Area from the use of helicopters is likely to be significant."

Proponent Daniel Hackett said he looked forward to providing the additional environmental assessment materials requested by Ms Ley, and believed the project could "set new and higher benchmarks" for the use of aircraft over the World Heritage Area.

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