Wonder why I waited all this time to finally see it. I was being snobbish about a good film. It has lots of imagery at play and especially the lake in Paraguay is mesmerizing. I suppose Wnendt got an idea for a scene in his crappy Wetlands from a dialogue of this movie.
To be honest, it's probably closer to a 3* given the underlying implausibility but taken on its own terms, it's intriguing throughout, sufficiently tricksy in the Chabrol manner and benefits from very engaging leads. So let's err on the side of generosity.