The country’s biggest municipal rock garden will be closed from Monday for up to six weeks.
Preston Park’s rockery pond sprung a leak several years ago, and it has become progressively worse.
For the first time in 30 years the pond, which was built in the mid 1930s, will be drained for the repair work..
The fish which live in the pond, including goldfish, golden orfe and koi carp, will be caught with nets and moved under expert supervision to two large containers on the site, which will be aerated and covered in protective mesh.
The pond will be drained, any debris removed and then people will get to work finding out where the leaks are and repairing them.
Councillor Pete West, chairman of Brighton and Hove City Council’s Environment and Sustainability Committee, said: “The completion time will depend on weather conditions, as repairs need to be carried out when the pond is dry.
“The work is being carried out in January when there are fewest visitors and the rockery will be closed off while work is under way for safety reasons.
“The repairs to the pond are part of an ongoing programme of improvements to the rockery.”
In April last year Blue Peter gardener Chris Collins unveiled the new-look rock garden and cascade, which could only be put into action temporarily because of the hosepipe ban.
The work included planting 5,000 bulbs and 300 trees, sanding down and repainting benches, renovating the chalk bank and constructing new steps to the chalet. Young offenders helped with the restoration project at part of the Community Payback scheme.