The Nanay is tributary to the Amazon River west of the Napo. It belongs entirely to the lowlands, and is very crooked, has a slow current and divides much into canos and strings of lagoons which flood the flat, low areas of country on either side. It is simply the drainage ditch of districts which are extensively overflowed in the rainy season. Captain Butt ascended it 195 miles, to near its source.
 A cano, like furo, is a kind of natural canal; it forms a lateral discharge for surplus water from a river.