The smell was overpowering. It drifted over in great waves, mixing with the salty tang of the sea air.

I was bobbing up and down in a small fishing boat off the coast of South Africa, and in front of me was Dyer Island, home to 40,000 fur seals and their yapping, newly-born pups.

Visitors pay $100 to meet sharks at close quarters

But it was not the putrid stench of dung and afterbirth that was uppermost in my mind.

What was my prime concern was the prospect of pulling on a wetsuit, clambering into a flimsy wire cage and being dunked in the sea among a school of rather hungry-looking great white sharks.

Dyer Island is one of the best places in the world to see great whites. Until a few years ago, it was the haunt of fishermen and the odd spear-diver.

Now it has become the focus for a booming tourist industry. In the little fishing village of Gansbaai, which faces Dyer Island, six companies now offer visitors the opportunity to go cage-diving with great whites.

Real-life Jaws

It has become surprisingly popular, earning Gansbaai, by some estimates, around $1m a year.

Steven Spielberg immortalised the shark with his film Jaws

Now I was about to become the latest visitor eager to part with $100 for the chance of an encounter with a great white - the animal immortalised in Stephen Spielberg's film, Jaws.

Swimming with a great white shark seems hardly natural, whichever way you look at it. The great white - Latin name Carcharodon carcharis - can reach a length of seven metres and weigh over 2,000kg.

At that size, it would be bigger than the boat I was now standing in. It eats small whales, dolphins, seals, turtles and other sharks.

But I was not to worry, skipper Jackie Smit told me. A great white is as likely to attack a boat as a lion is to attack a car.

If, by some stroke of ill-fortune, the shark got entangled in the ropes tethering the cage to the boat, there was a chance that it would panic and drag the cage down with it. There have also been cases of smaller sharks barging their way between the thin metal bars of the cage.

But that, Jackie assured me gruffly, was extremely unlikely.

Shark attack

We had not been anchored for long before the first shark appeared. It was a spectacular entrance - announcing its presence with a lightning attack on a southern fur seal not 20m from our boat.

Shark-watching: An alien experience

The seal, which comfortably weighed more than me, was tossed helpless into the air, flippers flailing, before disappearing beneath frothing sea water. It did not reappear.

It was a startling image, and one which I could not quite dislodge from my mind as I pulled on my wetsuit, mask and snorkel and prepared for my encounter.

With a weight belt round my waist making every step a clumsy one, I climbed over the brow of the boat and down a wooden step ladder into the drum-shaped cage.

The shock of jumping into the freezing south Atlantic was enough to take my breath away, let alone the anticipation of coming face to face with the creature they call White Death.

At first all was confusion. All I was aware of was the frenetic thumping of my heart and the hoarse sound of my own breathing through the snorkel.

There were two of us in the cage - me and a rather burly Dutch tourist called Marcel - and I had to concentrate hard to avoid bashing into him too much as the waves buffeted our flimsy wire refuge.

And then they appeared - first one, then another, emerging out of the green gloom, circling, turning, coming to within a hand's reach of the cage.

Each one was about three and a half metres long - comparative babies, but quite big enough for me. I peered in fascination, whilst trying to avoid poking any one of my limbs through the walls of the cage.

Was I terrified? Not really - not because I'm brave or foolhardy, but because the whole experience was too alien and ethereal; I felt as though I was watching a television documentary, albeit an enthralling one.

The sharks appeared serene, nervous even - certainly not the ravening monsters I had expected. They did not even reveal those cruel rows of razor-sharp teeth. They just looked, then swam away.

Diving controversy

Cage-diving with great whites in South Africa is not without its critics. Divers and surfers claim it is responsible for an increase in shark attacks along the South African coast - great whites, they say, are making a dangerous association between human beings and food.

Conservationists are critical of the way in which some operators bait the sharks with lumps of meat tied to a rope, teasing them and sometimes injuring them on the side of the boat or on propellers. Jackie Smit and other operators dismiss these fears.

They say there is no proof of a connection between cage-diving and more attacks. And they claim they are aiding people's understanding of a much-maligned creature.

"Some visitors come away with a near-religious experience," a Cape Town shark expert told me. "And if the sharks are worth more alive than dead, then so much the better."

So far, the jury is out on whether cage-diving has a negative impact on great whites, and more research is needed.