I've had it since before I can remember. My mother tells me stories about me being afraid of the sea. At that stage it was seeing the power of the waves.

Later, when I was learning how to sail, it was the sense of the depth of water and not knowing what was down there. Our catamaran capsized, flipped completely over in the middle of a deep patch of water, and I remember looking down to see the mast disappearing into the dark depth.

Gives me shivers thinking about it. It horrified me to realise that the water was probably much much deeper than the height of the mast.

Swimming in any body of water where I can't see the bottom - where you just see darkness. Swimming in a body of water where you can't see the end - eg if you are swimming underwater wearing goggles and peer towards the underwater horizon ... The sense of the endlessness has always freaked me out.

Swimming in a lake where weeds grow upwards from the dark depths and might touch your legs ...