Last week I bought a watermelon, and that day cut the rind of it. Also that day it was placed in a glass container, with a plastic lid that fits snugly around the glass on top, and stored in the refrigerator.

Today I went to finish it off, after not eating some for a few days, and was greeted by a 1/4 inch of milky white colored watery liquid in the bottom of the container, along with partly mushy watermelon innards.

I don't intend to eat it, but have had slightly mushy watermelon innards before, without the liquid described above. Anyone have any ideas what that is?

P.S I have seen What are the telltale signs of a bad watermelon? already, but as that is a general question about what to look out for and not what the above is, I am hoping that this answer will not be considered a duplicate.