Labrador rescue dog?

We have 2 Labs. Boz (the more lively of the two) loves water, but it
seems he has rescue tendenciees. We've had Boz since a pup, and he has
had no rescue training, so it must be inbred. His brother doesn't like
the water much. Besides, Boz does his best to keep his brother out of
the water! When our son swims underwater in the pool, Boz will jump in
to try and save him.

On a recent holiday, we found that Boz went crazy every time a
speedboat or canoe came past. He'd start making the weirdest whining
noises, and given half a chance he would rush into the water and swim
out to the boat. Only when our daughter feigned distress in the water
would Boz give up on the boat and come back to shore. In fact, he
becomes so panic stricken that his starts to shake.

Clearly he's not being naughty. He's just very unhappy when anyone or
anything is on/in the water. (Skiers make him especially panicky.) As
you can imagine, it is a problem, since he could get hurt swimming
across a busy river, or he could scratch a swimmer in the water.

The only conclusion I can come to is that he is a rescue dog by
genetics, although his brother has none of his tendencies. So, can
rescue tendencies be inbred in Labradors? Is there anything I can do
to reduce the trauma he goes through, other than not taking him
anywhere near boats and water - which would be very sad as he loves
swimming. (As a matter of interest he is quite happy to sit in our
boat, even underway. But if someone dives into the river, or if a
boat comes past, he's in the water in a flash!)

Can anyone give me any insight into his rescue behaviour? To be
honest, I'm proud of his rescue tendencies, and he really is a lovely
dog, but the noise he makes when he wants to rescue someone and we
hold him back, is unbearable!

Thanks.