The diesel spill was reported just over three weeks ago after members of the public noticed a strong smell coming from the lake. A number of swans were also found covered in diesel. The Council said affected birds were taken to Ambury Regional Park, in Mangere, before being taken to the Auckland Zoo for rehabilitation.
It was later determined the diesel had come from the North Shore Hospital grounds.
A spokesman said at the time that initial investigations showed the spill had come from a diesel fuel tank used to power the hospital's generators during a power outage.
The leak had happened during torrential rain which had overwhelmed the hospital's stormwater filtration systems.
Daniel said small pockets of "visible sheen" may still show up on the lake and members of the public were urged to avoid contact with any visible floating diesel.
"It's expected that weather and natural processes will continue to disperse and break down any remaining residue."
