Morning Scepticism: Drowning Man

If you happen to be walking past a lake and in there you see a drowning man, is it your obligation to help? I'm sure all talk of moral relativism or cultural sensitivity would go out the window in such a scenario, it would almost be unthinkable that there would be anyone out there who would consider such an action as problematic. This is why I think that an isolationist policy for a government is problematic. If there's the capacity to act to save lives and act for a greater good, then it's not really different to the problem of intervening to save the life of someone drowning in a river. Of course killing 20 people and wounding hundreds near a river on the notion of there being a drowning man is a different story.