If anyone is interested in a cruise on the Rio Negro, a friend of mine owns a boat (20m motor yacht, I think he calls it). The boat moors near Manaus and it has aircon cabins with ensuite shower/toilet.

His customers are frequently fishermen, sometimes TV crews use the boat for filming the rainforest and biology students from the USA recently started hiring the boat for field trips.

A group can hire the whole boat, or individuals can fill spaces where a group has only part booked the cabins.

It costs about $150 per day but this includes all your meals.