Right. So if it's more humid, then the density should increase because
the
water is participating in the transmission process, rather than sitting
in
the lake.

density is less, there is more energy so the air is more spaced out.

How does density decrease by ADDING molecules? As I said before, you're
talking about adding water molecules. So unless the volume is getting
bigger or the air molecules are being displaced, the density of air is
increasing.