[sinanju]

I’d say there’s a common M.O.

If they were accidents or suicides the whole bloated corpse would wash up. These deaders have been cursorily weighted down so that the sneaker-shod foot doesn’t float free until the body rots sufficiently.

[AnAmericanMother]

You're correct that I omitted the possibility of murder and body dumping.

But it's not true that drowning victims always float. There's a good deal of variation, depending on body mass, what the deceased is wearing, etc. In cold water (and this water is pretty cold - dry suit country) bodies may never resurface at all. There are plenty of cases in the Great Lakes of drowning victims from boating accidents, etc. where the bodies are never found.