Scientists say the angle is so acute that it is barely visible to the naked eye, but a 20-year study has shown it has slanted significantly since the late 1980s.

Dr Iloc Noturbi, who conducted the research, said the lean may have been triggered by a disturbance deep within the earth's crust, which has led to a gradual sinking of the lighthouse's foundation on one side.

The lean was discovered following an environmental study of the lighthouse on March 22, which mirrored an identical study carried out on March 22, 1989.

"At first I thought there could have been a shift in the sun's location, or my timing was wrong, a shift in the magnetic polls or even a variation in the Argonic lines," Dr Noturbi, from the Geo-omphalos Barycentre of Australia, said.

"But a further check at the same time on the following day proved that the shift at the top of the lighthouse was real."

Tourism officials hope the leaning lighthouse will spawn a craze in Wollongong similar to that created by the Leaning Tower of Pisa in Italy, whereby tourists pretend to prop up the structure while posing for photographs.

Safety issues aside, tourists at Flagstaff Hill yesterday were keen to embrace the leaning landmark.

"I've been to Pisa and posed with the leaning tower there, so this would be a nice addition to my photo album," Madge McCormack said, while moving her picnic blanket a little further away from the lighthouse's base.

Dr Noturbi said those wishing to see the angle clearly could hold up a plumbob or a heavy sinker on a piece of red or blue cotton next to the lighthouse, and look directly down the centre.

He said the lean was most obvious towards the edge of the lighthouse.

It was also important to remember that today was April Fool's Day, Dr Noturbi added.