For six-year-old Poppy Henderson and her parents, who make almost as much use of the green grass and shady tree canopies as they do of the pools, the plan comes as a blow.

"We would be devastated to see even an inch of these magnificent grounds lost," said Poppy's mum, Louise.

Similarly, former long-time manager of the pool, John "Tav" Taverner, whose father started as a lifeguard in 1947, and whose family managed the pool from 1956 to 2012 said he was "red hot fiery mad" over the proposal.

Mr Taverner also believed the construction of multi-storey units overlooking the pool and surrounding grounds would be unpalatable to a majority of the nearly 30,000 patrons who use the art-deco facility each summer.

A spokesman for the Giants confirmed there would be some land lost to the proposed development – an estimated 1200 of the Manuka Pool footprint of 7750 square metres.

But he said patrons would be compensated by having access to land to the south of the pool where the caretaker's cottage is.

"This space would be opened to the public during non-game times resulting in no net loss of land to the pool."

The land earmarked for redevelopment is the left hand back end of the pool grounds, which houses a number of storage containers.

The spokesman said that area would be upgraded to include a public gym, a health and wellbeing retail precinct and residential space.

The developers were well aware "the heritage assets on the Manuka Oval site are of immense significance to the Manuka community which is why our proposal is committed to preserving and, in many cases, enhancing, these assets".

While the plans were still being formed, the spokesman could not rule out that some of the established trees in the area could be lost to the development.

"This proposal seeks to keep as much of the existing tree-scape in tact as possible, particularly those heritage-listed trees. Several trees on the site have come to the end of their lives and, as a result, extensive space has been allocated in this proposal for the planting of new trees to renew the original landscape scheme and recognise the historic plantings of the site. We will have as minimal impact on the trees as we can and ensure there is space to replant and that landscaping is enhanced."

A spokesman for the ACT government reiterated that, as an unsolicited bid, the development had not yet been approved.

He also noted that the 2004 heritage listing of the Manuka Pool included "associated landscaped grounds comprising spacious lawns, trees and vegetated boundary fencing" which were "intrinsic to the heritage significance of the place".

"Any proposed work would need to be consistent with the existing registration documents and any Heritage Guidelines and Conservation Management Plans for each place - in the case of Manuka Oval, a key conservation objective is for the perimeter plantings to be maintained and enhanced."

The ACT government has also indicated it will uphold heritage listing protections for buildings within the Manuka Arts precinct, warning the developers the historic buildings would need to be incorporated into any new development.

The $800 million plan includes upgrading the oval and funding it through the wider redevelopment surrounding the oval which will include 1000 apartments up to seven-storeys high, commercial and retail space, and carparks.

For Poppy's dad, the need to develop Canberra should not cost it its heritage.

"As a fairly young and small city we just don't have that many places of genuine heritage value, so you would think we would move heaven and earth to protect the special places we do have and, quite frankly, I can't think of a more beautiful place in Canberra than this pool," Andrew Henderson said.

He did not agree with any land being handed over for a health hub and was extremely concerned about the impact of units looking down onto the pool and grounds.

Similarly, Tuggeranong writer Michael Weaver makes the 20-minute journey each week to Manuka Pool because of its atmosphere.

"It is the best outdoor pool in Canberra – it has an atmosphere which is unique and I feel an extra sense of enjoyment while swimming there."

Mr Weaver said the government should ensure the full Manuka Pool footprint and privacy was protected.

"I see it as a threat to the pool's character and heritage. We need to listen to what residents and the users who love this area have to say about it before we proceed any further down the redevelopment path."

Kingston and Barton Residents Group spokeswoman Rebecca Scouller said the Canberra community would rally to protect its "heritage gem".

"Do we want to surround the pool with the colosseum-like, 1000 apartment proposal by GWS and Grocon? She noted that parking near the pool would become nearly impossible.

"Manuka pool is part of Canberra's heritage heart. It is there for the benefit of all Canberrans, let's not ruin it for the sake of an apartment block."

The Giants' spokesman said community consultation was still being considered and anyone with concerns should make their feelings known.

"We will continue to engage the community about how we can ensure these assets remain in place for another 100 years," he said.