Four months after a man climbed the Sydney Harbour Bridge, sparking a massive police operation and causing hours of traffic gridlock, the NSW Government has announced it will increase fines for illegally scaling the bridge.

Multiple lanes were closed after Wayne John Cook, 43, climbed an arch in the morning peak hour in April.

It took almost six hours for crews to get him down.

At the time, Roads Minister Melinda Pavey promised there would be a review of security and that has now been completed.

"That event four months ago, showed that we needed to deliver some changes and we will be delivering those changes," she said.

The penalty for illegal climbers will be increased from $3,300 to $22,000.

Police lead a man down the Sydney Harbour Bridge where he had been for hours on April 4, 2018. ( ABC News )

It means the fine will now be the same for those who climb the Sydney Opera House.

"The Harbour Bridge performs an incredibly important function to the city and we don't want people taking it for ransom," the Roads Minister said.

"Whilst the community is sympathetic in terms of mental health issues, there also needs to be a strong message from us that's it's not acceptable for a community to have to go through this."

The review found the fencing on the walkway and the bike path were adequate, but security around the train line will be increased.

Fencing along the rail line will be made higher and the anti-climb mesh will be extended.

There will also be more security cameras installed.

A man climbed the Sydney Harbour Bridge and was up on the beams negotiating with police for hours on April 4, 2018. ( AAP: Mick Tsikas )

Even with the new measures, the Minister concedes the bridge can never be 100 per cent secure.

"It is impossible to cover the whole entire bridge to ensure no-one can access at a point," Ms Pavey said.

The changes should be in place in three months and there will be rail outages to make the modifications.

The number of security guards will not be increased.