The footage shows two dogs, who appear to be trying to herd sharks, in the ocean near the West Australian town of Broome.
Russell Hood-Penn describes what is taking place as he films.
"The dog's biting the shark," he said. "The dog is under the water with the shark. What the hell! That is unbelievable! I've seen it all now."
The video called "dog has a ride on a shark" now has more than three million views on YouTube.
"I would just like to say thank you to everyone who has taken an interest in my video, the response has been amazing, i (sic) would really like to urge anyone who is thinking of travelling to Australia to include Broome and Cape Leveque in your trip as they are really amazing places," he says on his blog
Hood-Penn and his wife spent about five months travelling around Australia. At one of their stops a woman told them that if they went to a certain area at high tide they might see dogs swimming with sharks.
"So off we went down there and sure enough ... there were these two dogs and they were swimming with the sharks, they were swimming out maybe 50 or 60 metres and it almost looked like they were rounding the sharks up and bringing them to the shallows," he told the Sydney Morning Herald.
"We were there watching it for 20 or 30 minutes ... and right when I decided to take the video the dogs swam in and then one of the dogs just dove down and grabbed hold of the shark's tail and went for a swim in the water with him."
The sharks are believed to be lemon sharks, which grow to be about three metres long.
Hood-Penn said his video was better marketing for Australia than what was done by Tourism Australia's official adverts, which had "too much cheese."
"That certainly is an amazing piece of footage, but I don't think vision of sharks practically on the beach is the right image to entice people to Australia," John Lee, chief executive of the Tourism and Transport Forum, told the Sydney Morning Herald.
Near the end of the video Hood-Penn remarks that the sharks were probably coming in because there was a dugong, which had been "speared, ready for the dinner plate" on the beach.
"Great Video, until i saw the last minute, DUGONGS ARE ENDANGERED PROTECTED !!!!! really tough guy spearing one of the slowest animals in the sea!" commented a viewer going by the name demografixjw under the YouTube
Dugongs, which some people believe inspired tales of mermaids, are threatened.
"These languid animals make an easy target for coastal hunters, and they were long sought for their meat, oil, skin, bones, and teeth," reads the information on the National Geographic
website. "Dugongs are now legally protected throughout their range, but their populations are still in a tenuous state.