Poynton Pool is classed as a large high-risk reservoir, which means an uncontrolled release of water could endanger human life.
The council, as landowner, has a legal obligation to carry out works to ensure the reservoir is safe and, following a safety inspection, has now submitted a planning application to do that work.
But residents are furious, arguing the pool has never overflowed or breached the dam since it was built more than 250 years ago.
The campaign group, Friends of Poynton Pool, is fighting to protect the trees and wildlife and demanding the most environmentally-friendly solutions are carried out, should any works be undertaken at the pool.
The group says its own expert has ‘blown holes’ in the 2019 report done for the council.
And it argues the £1.38m the authority is planning to spend on the works is unnecessary and could be scaled back.
Campaigner David Massingham told the Local Democracy Reporting Service: “We think that possibly there is some work needed but we don’t believe that the scope of works that’s been prescribed by Cheshire East is the correct one.
“They need to do a new section 10 inspection and the new inspection would need to take account of all of the information that we’ve now collated and put in front of Cheshire East.”
He said despite the Friends of Poynton Pool submitting evidence from one of the best qualified professors in the country, this has been ignored by the council.
Last month, despite the opposition, Cheshire East submitted the planning application for the £1.38m scheme.
The council is seeking permission to remove low points along approximately 480m of the Poynton Pool dam embankment and to slightly raise the level of crest to increase the flood resilience of the reservoir.
It says a kerb alongside an enhanced footpath will create the crest level and the works will also include the creation of two 40m-wide clearings, to further increase flood resilience.
Initially the work would have seen the destruction of more than 80 trees. The council says this number has now been reduced to 31.
But objectors are sceptical.
Mr Massingham said: “We don’t believe the alteration in the number of trees being affected. Cheshire East have not changed the scope of works. Now, if they’ve not changed the scope of works, how can they say that 50 trees are not going to be affected?
“I’m a construction professional, I spent my life in construction, so if you don’t change the scope of works, surely the impact is the same as it was when you started.”
The application, number 23/4152M, can be viewed on the planning portal on Cheshire East Council’s website.
The last date for members of the public to submit comments is December 27.