There was a case in QLD where a diver Gabe Watson was found guilty of manslaughter because the court found that as an experianced rescue diver he failed in his duty of care to resuce his buddy (wife) who drowned in unusual circumstances. The conviction was controversial because he was originally facing a murder trial but instead pleaded guilty to manslaughter and was given a reduced sentance. Regardless however, it does appear that in QLD at least, even when on a recreational dive you still have a duty of care which increases with your level of certification.
There is a 5,000 page thread somewhere on Scubaboard devoted to that case
I read that thread carefully, and I came away with a slightly different impression. The judge did indeed say something like that, but the attorneys on the thread had a lot to say about that. Here are some highlights as I understood them.
1. He was
not "found guilty of manslaughter." He
pleaded guilty to manslaughter, and that is important, as I will point out later.
2. The judge's statement is not founded in law or in the evidence, and pretty much everyone was confounded by it. Even in QLD, there is no law that says a recreational diver has a duty to care. The only reference to it is in the judge's interpretation of an agreement made between the prosecution and the defense.
3. In countries (like both the U.S. and Australia) that use precedent setting cases as guidelines for future decisions, one might be concerned that this judge's statement might be considered precedent and influence future cases, but it will not. Precedents can only take effect if the decision is the result of a full judicial process,
not a plea bargain. If Watson had been "found guilty," it would have set a precedent. Since he was not found guilty, it does not.
Again, I am not an attorney and am just summarizing my understanding of what the participating attorneys said.
I will however repeat a challenge that has been made many times: search legal history and see if you can find a case where a nonprofessional diver who happened to be the vicinity of an incident was successfully sued. I am not sure you would find a case where one was unsuccessfully sued, either.