Pollutants in water close to dredging operations for the Disney project have reached double the levels predicted, official tests show.
The higher-than-expected levels had led to a threefold rise in the number of fish dying in the area, fishermen said.
Officials from the Works Bureau confirmed that levels of suspended solids in the area were 72 milligrams per litre - almost double the worst-case scenario predicted in an environmental impact study before reclamation started in July.
However, environmental consultants from the Government and the contractor say preliminary tests found insufficient evidence to prove dredging or dumping caused the fish deaths.
A Works Bureau spokesman confirmed more tests would be conducted.
But an environmentalist said dredging might have to stop if the activity was confirmed to have caused the rise in the level of suspended solids affecting the ability of fish to breathe.
Chairman of Ma Wan Fishery Rights Association, Lai Tak-chuen, said: 'Between 20 to 30 per cent more fish were killed after the reclamation works commenced. Other than the reclamation work there are no other major construction projects nearby.'
Mr Lai said the number of fish found dead every day since reclamation began had jumped from two or three to 10.
The Environmental Impact Assessment Report on Northshore Lantau Development predicted in a worse case scenario that the Ma Wan Fish culture zone would see suspended solids elevations of 39.9mg per litre. Mr Lai said officials last week told them test results showed more than 50mg per litre - a trigger level which allowed fishermen to be granted ex-gratia payments.