The Yapura. West of the Rio Negro the Amazon river receives three more imposing streams from the north-west -- the Yapura, the Ica or Putumayo, and the Napo. The first was formerly known as the Hyapora, but its Brazilian part is now called the Yapura, and its Colombian portion the Caqueta. Barao de Marajo gives it 600 miles of navigable stretches. Jules Crevaux, who descended it, describes it as full of obstacles to navigation, the current very strong and the stream frequently interrupted by rapids and cataracts. It rises in the Colombian Andes, nearly in touch with the sources of the Magdalena, and augments its volume from many branches as it courses through Colombia. It was long supposed to have eight mouths; but Ribeiro de Sampaio, in his voyage of 1774, determined that there was but one real mouth, and that the supposed others are all furos or canos. In 1864-1868 the Brazilian government made a somewhat careful examination of the Brazilian part of the river, as far up as the rapid of Cupaty. Several very easy and almost complete water-routes exist between the Yapura and Negro across the low, flat intervening country. Barao de Marajo says there are six of them, and one which connects the upper Yapura with the Uaupes branch of the Negro; thus the Indian tribes of the respective valleys have facile contact with each other.
 A furo is a natural canal -- sometimes merely a deviation from the main channel, which it ultimately rejoins, sometimes a connexion across low flat country between two entirely separate streams. A cano, like a furo, is a kind of natural canal; it forms a lateral discharge for surplus water from a river.