About 20 years ago an amazing new opportunitiy opened up in Western Australia when we were able to swim with whale sharks for the first time and now a new development means it’s finally possible to swim with humpback whales in Australian waters, too.

What’s it like to be in the water with a creature many times your size?

When the skipper called “it's coming straight towards you – jump,” we jumped. At first, nothing was visible. But as the bubbles cleared and I peered into the deep blue, the butterflies in my stomach turned into eagles. A giant shape, maybe seven metres long and propelled by gentle sweeps of its huge tail was heading straight towards me. It was the world’s biggest fish – a whale shark.

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Whale sharks can grow up to 18 metres long and weigh up to 40 tonnes!

Fear fled, replaced by a sense of wonder as the huge yet harmless creature swam in the middle of our group and played around us. For the next two hours it was as if we had adopted a puppy the size of a truck. As I floated on the surface it brought its mouth about 30 cm from my face and opened wide. It looked as if it had been caught in a horizontal vice, its mouth stretched more than a metre across with an eye at either end. When he opened this expansive maw I was left staring down a vast well of flesh, pulsating as his gills fibrillated. There was a fish of edible size living about a metre down his throat.

That was the moment I knew why I didn't become a dentist.

I backed away from the gaping mouth but the shark advanced. I circled. The shark circled. The scene was starting to remind me of a school dance. Then another swimmer came close and the shark shifted his attentions to her. I swam back to the boat to change memory cards but once back in the water I found the shark waiting for me. It was like having a pet submarine.

That morning was remarkable but it required no special skills. If you can tread water and snorkel you can meet whale sharks. Some encounters may be fleeting, others may swim slowly so you can keep up and others may be curious.

Whale sharks are the world's largest fish – up to 40 tonnes and 18 metres long. They are also completely harmless. Like many whales, they live on tiny krill – not fish, seals or people.

From about March to July each year, many whales sharks turn up along the Western Australian coast near Exmouth. Created in 1967 as the support town for a US Naval communication base: now the surrounding ocean has brought tourists keen to experience the delights of Ningaloo Reef.

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Imagine being this close to the largest fish in in the world! (Photo: Exmouth Diving Centre/Facebook)

The reef is teeming with marine heavyweights and huge schools of baitfish; a parade of humpback whales passes from July to September and nesting turtles from November to February.

But when I think of Exmouth, I see that big, toothless mouth. And I think of an inattentive girl who was also on the trip being swept aside by the whale shark's tail just like a pawn off a chess board. The shark dived and the girl apologised. She later said that she wasn’t hurt but it felt like a giant hand pushing her aside.

The exact season varies depending on the time of the spawning of the coral of Ningaloo Reef.

Anyone who encounters the world’s biggest fish will never forget the experience.

Whale sharks migrate to Ningaloo Reef in WA every year, giving visitors a once-in-a-lifetime experience

Exmouth Diving Centre pioneered swimming with whale sharks in a less-intrusive way. A day trip with the whale sharks costs from $399.

While you may need to be planning your whale shark encounter now for next year, the season of the next big thing is about to begin. Sunreef Mooloolaba initiated swimming with humpback whales on the Sunshine Coast between July and October each year. It costs $149 for a half-day swim and the experience is closely regulated.

There are a few big advantages in going for a swim with whales over taking a whale watch cruise. The cruises are required to stop 200 metres from the whales and then hope the whale comes closer. For the swim the distance is reduced to 100 metres or less so you start a lot closer. The obvious advantage is the incomparable thrill of being in the water with one of the world’s largest living creatures.

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The Ningaloo Reef is great for whale watching too (Photo: Exmouth Diving Centre/Facebook © Kiss the dolphin)

This year will be the first year that swimming with humpbacks will be trialled in Western Australia too. See Exmouth Diving for details. It begins in August 2016. The whale watching tour costs $110 plus $145 extra for the swim option.

The first place to offer swimming with whales in Australia was Far North Queensland where dwarf minke whales come each winter (mainly June and July). These are smaller than humpbacks – up to eight metres – but can be very curious. Several operators offer swims with minkes: see the Great Barrier Reef Marine Park Authority for a list of operators.

Have you ever swum with sharks or whales? Would you give it a go? Join the conversation below!