I downloaded the Natural Earth Data rasters at 10m resolution. These come with or without water. I prefer to use the version without water for some reasons.
However, in these versions, I find that even small islands turn up as blotches and land-masses which have a strait between them become joined as seen in the images below from their download page:
I suspect that the border of the bodies is being drawn with a thick pen or something.
Is this a bug, or made so for some valid reason?