It's a very common problem. Most digital cameras will eventually develop a few stuck pixels on the CCD, if they don't already have any. Google "stuck pixels" and "hot pixels". They can be red, green or blue (sub-pixel), as well as white (whole pixel).
Some cameras can be remapped, which disguises the problem - but it wouldn't be a cheap job.
You've got a second small white pixel - between the two buoys.
For your best pics, it'll be worth cloning out the dodgy pixels with an editing program, or you could try an automatic hot pixel remover. I haven't found one that works very well, though, except for Silkypix with RAW images.