For the Nanay people of Siberia, see Nanais.

The Nanay River is tributary to the Amazon River west of the Napo in Peru. The Nanay is one of the three rivers that surround the jungle city of Iquitos, making it an island. Other nearby settlements on the river include the villages of Santo Tomás, Padre Cocha, and Santa Clara. During periods when the river is low, the many beaches along the Nanay are popular destinations. The Nanay belongs entirely to the lowlands, and is very crooked, has a slow current and divides much into canos¹ 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.

[1] A cano is a kind of natural canal; it forms a lateral discharge for surplus water from a river.