SOLVED. Girl Lives on River/Goes Down River/All is Fake, Some Kind of Zoo or Spaceship? [s]

[Melissa]

The topic description sums it up pretty well.
A pre-teen or teen girl lives in a pre-industrial village near a river. She travels the river - maybe in a canoe? - and finds other communities like hers, and eventually learns that they are all in some kind of experiment - maybe it's a zoo or a spaceship?
I remember the old paperback I read had lovely artwork on the cover, a river with a heron, all browns and golds

[Lobstergirl, au gratin]

When do you think the old paperback dated to? YA or adult?

[Melissa]

It was probably from the 80s
The village she lived in was huts

Driving me nuts - I'm going to go back through my read books soon if someone doesn't remember before me

[Melissa]

Found It!
Moon-Flash
(I was wrong about the heron on the cover - What book was that? Now *that's going to drive me crazy lol)