Dorsal fins slicing through the glass-like water off Warners Bay, flashes of white bellies under boats near the Swansea Channel entrance, circling off the jetty at Murrays Beach and powerful breaches off Marmong Point and Pulbah Island.

But do the sightings, and they are almost being reported every other day, mean there is an increase in shark numbers or an increase in the awareness.

The Department of Primary Industries shark expert, Dr Vic Peddemors, said there were at least two great white sharks enjoying themselves in Lake Macquarie right now.

But there may be more.

‘‘It is absolutely a massive ecosystem and it is varied. The power plants pumping in warm water would inevitably change the system there a bit,’’ Dr Peddemors said.

‘‘There is such a variety of habitats within the lake and the positives that come from that is things like the resident pod of dolphins, and the number of sharks.’’

Dr Peddemors’ first trip to Lake Macquarie was last year after the Newcastle Herald revealed footage of a great white cruising in very shallow water off the popular swimming spot at Murrays Beach.

He was impressed by the place.

‘‘I didn’t realise how big the lake actually was,’’ Dr Peddemors said.

‘‘Our aim at that stage was to come down and locate the shark to see if we could catch it and lead it out to sea.’’

It didn’t happen and the shark disappeared, although news that a fisherman caught it and killed it remain unconfirmed and unlikely.

It probably just swam out and moved on.

Since then, there have been dozens of sightings of various-sized great whites, all appearing to be in good health and inquisitive.

Theories for the sightings have included the banning of professional fisherman from the lake in 2002, allowing fish stocks to increase and, in turn, allowing it to support apex predators such as great whites.

‘‘Historically we had thought great whites were coastal, then we found them travelling immense distances by using tracking devices,’’ Dr Peddemors said.

‘‘We are also finding out more and more that they go into the shallow water areas like Lake Macquarie, like Port Stephens, like Sydney Harbour and the Hawkesbury River.

‘‘If you said that 20 years ago, people probably would not have believed you.’’

He later said: ‘‘I am a great believer that animals only move for food or reproduction. So if there is a lot of food around, there is no need for them to move.’’

The invention of the smartphone has also helped gather credible information, with most people now in possession of a camera and video player in their pocket or their purse.

‘‘And pretty much everyone is on social media,’’ Dr Peddemors said.

‘‘It is a totally new world out there.

‘‘The rule that social media has got on reporting shark sightings and shark bites is going to be very difficult to untangle.

‘‘I don’t think there are more shark bites than 10 years ago, I think we just hear about more of them.’’

But are there more sharks.

‘‘I would like to believe there is; they have been protected since 1990,’’ he said.

‘‘But sharks are like mammals, they reproduce very slowly. 

‘‘It takes a long time to recover from a depleted state.’’

And do they pose a threat to lake users in the lead-up to summer?

‘‘They are all juvenile white sharks. Although 2 metres, to most of us, is a really big fish, these guys are just juveniles,’’ Dr Peddemors said.

‘‘However, they do have the potential to be dangerous.

‘‘Fortunately no one has been bitten, touch wood, but obviously it is going to be on the top of everyone’s mind when the lake is used by so many people.

‘‘It is a worry but we can’t catch every fish.

‘‘There are bull sharks in there, there is everything in the lake.

‘‘Just because there is a white shark in there does not automatically put people onto the menu of food selection.’’

The last recorded shark attack in Lake Macquarie was in 1946, when a swimmer was bitten on the upper leg and buttocks in muddy water off Marks Point.

And it appears the current residents of Lake Macquarie are getting more than enough fish and other sharks to eat.

In fact, Dr Peddemors said the well-versed theory that all great white sharks moved on from fish to larger prey, such as seals, once they reached  the size that have been seen in the lake,  is now being questioned.

In fact, some tests on shark tissue  suggest some sharks never graduate from fish to mammals.

‘‘This is all relatively new understanding. 

‘‘Everyone has heard from people, including me, that there is a change in diets of white sharks,’’ Dr Peddemors said.

‘‘From fish to seals, for example. 

‘‘But to be accurate it is going from solely fish to mainly fish with possibly a few seals.’’

​