I know that for cars on the road they are not allowed to pass closer than a car width to you if you are on a bike (yes, I am a militant cyclist...) - and if they do and you just happen to have your bike keys in your hand and they slip down the side of the car then even with a stretched arm you are going to win in court as the car was closer than it legally should have been.... (I've been across too many car bonnets to care too much about cars so just chill now and ride defensively - ie lots of braking and assuming that the car driver will do something mad like overtake and then take a sharp left [happens everyday...])
So perhaps .. well lets say that the range of a speargun is 5m... if a craft is within 5m of you then they are too close and especially if you happen to see a large bass on the surface about, lets say 5m away and you just happen not to hear the craft... unfortunate as you did have a clear flag up to say you were diving/hunting ... :0)
(PS I in no way advocate violence - it would just be an unfortunate shot
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