An MP has called for plans to build almost 100 new homes at a reservoir to be rejected at a public inquiry.
Thames Water lodged an appeal after a revised bid for Reading's Bath Road site, which it wants to sell to developers, was rejected last October.
Reading West MP Alok Sharma has written to the government planning inspector who will make the final decision at a public inquiry in November.
Thames Water said it has made a number of compromises to its plans.
Save the Bath Road Reservoir Group believes Thames Water could turn the area into an educational resource for local schools.
The group also claims the vegetation covering the underground reservoir, which is closed to the public, is a haven for wildlife such as deer, foxes and badgers.
In the letter to the planning inspector, Mr Sharma said: "The development would change the area immeasurably.
"A townscape like Reading needs green areas to provide a balance."
He also questioned the application which includes 40% of the units being flats when he said Reading's most "pressing" need is for family homes.
Councillors listed 12 reasons when they threw out the revised plans last year, which included worries the development would have had a detrimental impact on wildlife.
But Thames Water, which first submitted an application in 2008, said in a statement: "We have listened to local people and made some changes, just not all the things they wanted [some of which, like retaining embankments, were physically impossible].
"We think the best way ahead is for both sides to present their case to a public inquiry and see what an independent inspector recommends."