Sea based rectena

Yes, your gut was right. That is a stupid question. ;-)

The microwave frequencies proposed are pretty much the same
frequency as you get in microwave ovens.

Bearing in mind you're even asking this question I can
only assume you don't have a microwave oven. Microwaves
penetrate food in a microwave oven to a cm or two at
most- they're mostly absorbed by the water in the food.

That's why rain absorbs and scatters it of course. A meter
under? Forget it; unless you want to boil the water and
go through the steam cycle, but then you'd have to deal
with people justifiably talking about this death ray
you'd built.