There ARE some true lents out of the Rio Orinoco, but they are few and far between. Actually one of my fav. pictures of a female lent. actually came from the Rio Orinoco. That was several years ago though, and since then I can't find the pictures on the net to save my life. They were hott though!!
The Rio Negro is going to get you the best looking lents if you ask me...lol. I'm curious to see the lents from Rio Amazonas, Rio Branco, and Rio Essequibo. That would be really interesting. The problem right now is most 'lents' are being imported out of the Rio Orinoco at the moment.
I know that the best looking marms IMO come from the Rio Trombetas.