I went to the Laguna Azul, or Blue Lagoon, today. It is a fresh water lagoon in the mountains near Tarapoto. You get there via a jungle dirt track that goes up a mountain pass and across river Huallaga, an afluent of the Marañon, itself one of the two rivers that meet in Nauta to form the Amazon.
The river Huallaga at this point is about as wide as the Thames in London, flows way faster and carries a lot of vegetation ripped from its banks, including whole trees. There is no bridge, only a barge attached to a cable that runs between the two banks. The barge can take several cars or even trucks. It looks impressive but the system is quite smart. By adjusting the cables the barge can be oriented against the stream and by orienting it one way or another, it is actually the river's current that makes it travel across. The barge is sturdy enough to take a direct hit from a fast floating tree trunk without harm.
The lagoon itself is just beautiful, quiet and laid back, as if coming straight out of a glossy holiday brochure. As the region is still off the standard tourist routes and it is not the high season, our small group nearly felt like we had the place to ourselves.