As well as the sanctuary, it will also deliver nearly 100 sq m of new reedbeds and wildflower habitat, supporting wetland birds, amphibians and reptiles.
Temporary fencing will be installed while vegetation becomes established.
Alderman Gregory Jones KC, chair of the Hampstead Heath, Highgate Wood and Queen’s Park committee, said the sanctuary would provide a vital refuge for species already relying on the pond.
“This important project will create a peaceful sanctuary for wetland birds right in the heart of Hampstead Heath,” he said.
“By removing the causeway, we’re giving species like mallard, coot, grebe and swan a safe space to feed, rest and nest – free from human disturbance.”
He added that new reedbeds would strengthen nationally important ecosystems while naturally storing carbon.
“As they grow, the reeds will absorb carbon dioxide and lock it away over time,” he explained.