I had this with skyrim as well and never did figure it out but it's bothering me that it's here too. When I'm in the water or near water sometimes, especially noticable now since waves refract light, there is sometimes a random invisible dot that creates ripples in the water and moves in parallel with the character. It can be various distances or orientations as well. I don't have a picture right now but I'll snap one next time I see the issue. I'm sure I'm not the only one to have noticed this before though.