Deep Spirits

First a short story:

man who is a very good swimmer is taking a walk when he notices a boy, who apparently can't swim, in the water. The boy is struggling to stay afloat, he is screaming and yelling for help.

The man realizes that he could easily save the boy, and that there is no real danger to him personally if he does so, but he decides not to. After all, he had nothing to do with the boy falling into the water, he thinks to himself, and besides, he knows the water is cold and he doesn't want to risk catching a cold. It would be inconvenient.

He continues his walk, ignoring the boy's calls as they fade out.

THE END

Obviously the man is apathetic, callous, and so on... I believe there is no need to debate that.
The question is, do you believe the man had a moral obligation to save the boy?
If so, then would you say that he should have the legal obligation as well? What are your thoughts?

Sabina