Researchers from City University on Wednesday said they have found a lot more coral in Victoria Harbour than they expected, adding that this shows the water quality has improved in recent years.

The university's State Key Laboratory of Marine Pollution said its scuba divers have mapped five important coral habitats along the harbour, with the biggest site at Fat Tong Chau totalling 10 hectares in size - equivalent to 14 football pitches.

Jeffrey Chung, the manager of the project, said areas around Cape Collinson Lighthouse and Devil's Peak were also alive with coral.

He said they were amazed to have recorded a total of 35 coral species, along with some rare organisms like double-ended pipefish in the harbour in the past two years.

"All of our teammates were surprised by such diverse and large-sized habitats found in the Victoria Harbour because it is a highly developed area and many coastlines have been filled, but we could find so many organisms and habitats in the natural part [of the harbour]," he said.

Chung said their findings show that the government's Harbour Area Treatment Scheme is successfully cleaning up Victoria Harbour, but there is still room for improvement.

"We hope we can see the habitat expand in the future. Some artificial shorelines are included in our study, but we didn't find any octocoral or hard coral over there. In the future we hope we can find such organisms there because it means that the harbour area, the habitat and the water quality are recovering," he said.

The researcher said he hopes their study results will help authorities to better manage the harbour's water quality and conserve the marine biodiversity.