Campaigners have voiced their dismay over plans to build a secure children's home at a waterworks.
London Councils want to build a home for vulnerable children - the first of its kind in the capital - on part of the Thames Water depot on Lea Bridge Road in Waltham Forest.
But a campaign had wanted to turn the site into a park with swimming ponds and a forest school.
London Councils said an initial consultation would be held on Thursday.
The authority plans to use funding from the Department for Education (DfE) to build the secure children's home on the land, owned by the government.
It would house 24 highly vulnerable children with complex needs, along with up to four children who no longer need a secure environment.
The service, for which there is a national shortage, does not exist in London and means children currently have to travel a significant distance away from the city.
But Abigail Woodman, of the East London Water Works Park campaign, said there would be huge benefits if the site was to become a community park with wild swimming, a forest school space, arts and science buildings and dry and wetland habitats for wildlife.
Analysis for the charity predicted it would bring £18.5m in economic, social, tourism and environmental benefits.
Ms Woodman told BBC London: "Local people have been working for a really long time on this project. We've been talking to the landowner, which is central government, and they've known we've been putting these plans together.
"Waltham Forest and Hackney councils have known, so we were really taken by surprise at some point this year they're going to submit a planning application for a secure facility for children."
The charity is asking for an urgent meeting with the Pan London Secure Children's Home Programme.
Meanwhile, London Councils, the collective of the capital's boroughs collaborate, said the site was identified as the only suitable location to build the facility and a planning application has not yet been submitted.
A spokesperson said: "London boroughs are taking forward proposals to deliver a much-needed secure children's home that will provide specialist care for London's most vulnerable children. There is currently no facility of this kind in London."
They added if a planning application was submitted it would include details of the other sites that were considered, and that the DfE is obliged to consider alternative educational or public sector uses for the site it manages prior to considering a commercial proposal.
Local authorities place children in secure children's homes when no other type of care placement can keep the child safe.
They provide a safe environment where children can receive the specialist care, education and support they need.
An initial public consultation over the secure home is set to take place at Lee Valley Ice Centre on 7 February.
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