rotten stinky floating egg

[ontheDLo]

My hens have been laying for about 2 years now and it's dandy. Today I got my first stinky egg. As I was washing them off I noticed a foul smell and also that it was floating in the water I was cleaning with.
Any idea why this would have happened? I imagine it could be a one off, but curious if it is indication of a sick bird?

thanks!

 

[im2clumsy]

same with us......we had 1 bantie and 1 duck egg do the same thing.....we are still looking for answers....this all happened in the past few days----the duck egg would have been fresh last night between 7:30pm and 6:30 am. bantie is about 1-2 years old (not sure which one it was) ducks are still under a year old
The bantie egg was less than a week old.
From Central Illinois---our birds are free range in pasture with goats--just seeing if we've had anything in common--help you and I both find answers