[Texas Mom]

I hate to be morbid, but could these be old bodies from graveyards?

You're not being morbid. It's a possibility.

[burzum]

I hate to be morbid as well, but I doubt it. From what I've learned talking to police, if someone drowns, they initially sink (perhaps from the water displacing air in the lungs?). Then about two or so days later, they float to the surface due to the gases created in their bodies from decomposition. Later, they will sink again when the food for bacteria decreases and the porosity of their bodies increases. This is useful information for operations where police rescue people who drown in lakes (keep the boat around for about 3 days and wait for the body to float). Most of the dead from the graveyards would probably be past the point where the decomposition gases caused their bodies to bloat and therefore float (though I think it takes several weeks to get to that point--i.e. the Laci Peterson case).