Swimming with a dolphin may sound like a magical experience - but scientists say life seldom turns out well for solitary dolphins that seek human company.
Surprisingly, sex is often a motivator - and people have been injured and even killed in human-dolphin interactions.
The sight of a female bottlenose cavorting with swimmers in Manly this holiday season is the latest in a phenomenon that was first reported in ancient Greece 2000 years ago, according to a paper in the Aquatic Mammals journal in 2005.
More recent examples of ''solitary, sociable dolphins'' include Beaky, which set up home around Cornwall, England; Fanny, which based itself near Marseille, France; and Randy, which spread its time between England, France, Belgium and Holland.
''These encounters may be rewarding for both the dolphin and the people concerned but negative outcomes, particularly for the dolphin, are common,'' the journal report concluded.
One of the article's authors, Mike Bossley, said there was a need for ''dolphin etiquette'' and protocols for managing such interactions. He said when the dolphin became solitary they still had a social need and, instead of hanging out with other dolphins, people were often a substitute.
''Certainly the prognosis for them is not at all good. It almost always ends with the death of the animal,'' he said. ''The less encouragement to socialise with humans that can be given the better. Definitely don't feed it, that almost always leads to disaster.''
Arousal towards humans and generally aggressive behaviour has been recorded in solitary male dolphins.
Behaviour between dolphins can be very boisterous, particularly in association with sexual activity and, if directed at humans, has the potential to cause severe injury or even death.
''Similar behaviour in female dolphins is not common but has been reported. For example, Jotsa in the former Yugoslavia physically attacked human females who attempted to intervene in her interactions with human males,'' the Aquatic Mammals article said.
When a male solitary dolphin called Tiao was harassed by a swimmer in 1994 in Sao Sebastiao, Brazil, it responded by butting the man in the abdomen, a blow that proved to be fatal. Tiao also injured many other swimmers, earning the nickname ''killer dolphin''.
Simon Allen, who is studying for a PhD in dolphin-fisheries interactions at the cetacean research unit at Murdoch University in Perth, had similar concerns for the Manly dolphin's wellbeing.
''I don't like to be pessimistic but it's generally bad news for dolphins when they do this because people can't help themselves, and they [dolphins] end up dead because people feed them, they can lose natural feeding skills and become more and more boisterous towards people,'' he said.
''Even a juvenile might be 150 kilograms and people are, ironically enough, just as safe swimming with a shark of the same size.
''They are very strong: a small nip or a bite from a dolphin is painful and they do this ramming thing or they can whack with their tails. It is unlikely but it is possible, especially if they excited.
''People that get into the water with them need to think carefully about what they are doing.''