The Madeira river has its junction with the Amazon river 1400 km (870 miles) by river above Para, and almost rivals it in the volume of its waters. It rises more than 15 m (50 feet) during the rainy season, and the largest ocean steamers may ascend it to the Fall of San Antonio, 1070 km (663 miles) above its mouth; but in the dry months, from June to November, it is only navigable for the same distance for craft drawing about 2 m (from 5 to 6 feet) of water. According to the treaty of San Ildefonso, the Madeira begins at the confluence of the Guapore with the Mamore. Both of these streams have their headwaters almost in contact with those of the river Paraguay. The idea of a connecting canal is based on ignorance of local conditions. San Antonio is the first of a formidable series of cataracts and rapids, nineteen in number, which, for a river distance of 420 km (263 miles), obstruct the upper course of the Madeira until the last rapid called Guajara Merim (or Small Pebble), is reached, a little below the union of the Guapore with the Mamore. The junction of the great river Beni with the Madeira is at the Madeira Fall, a vast and grand display of reefs, whirlpools and boiling torrents. Between Guajara-Merim and this fall, inclusive, the Madeira receives the drainage of the northeastern slopes of the Andes, from Santa Cruz de la Sierra to Cuzco, the whole of the south-western slope of Brazilian Matto (irosso and the northern one of the Chiquitos sierras, an area about equal to that of France and Spain. The waters find their way to the falls of the Madeira by many great rivers, the principal of which, if we enumerate them from east to west, are the Guapore or Itenez, the Baures and Blanco, the Itonama or San Miguel, the Mamore, Beni, and Mayutata or Madre de Dios, all of which are reinforced by numerous secondary but powerful affluents. The Guapore presents many difficulties to continuous navigation; the Baures and Itonama offer hundreds of miles of navigable waters through beautiful plains; the Mamore has been sounded by the writer in the driest month of the year for a distance of 500 miles above Guajara-Merim, who found never less than from 10 to 30 feet of water, with a current of from 1 to 3 miles an hour. Its Rio Grande branch, explored under the writer's instructions, was found navigable for craft drawing 3 feet of water to within 30 miles of Santa Cruz de la Sierra -- a level sandy plain intervening. The Grande is a river of enormous length, rising in a great valley of the Andes between the important cities of Sucre and Cochabamba, and having its upper waters in close touch with those of the Pilcomayo branch of the river Paraguay. It makes a long curve through the mountains, and, after a course of about 800 miles, joins the Mamore near 15 degrees southern latitude. The Chapare, Secure and Chimore, tributaries of the Mamore, are navigable for launches up to the base of the mountains, to within 130 miles of Cochabamba. The Beni has a 12-foot fall 18 miles above its mouth called "La Esperanza"; beyond this, it is navigable for 217 miles to the port of Reyes for launches in the dry season and larger craft in the wet one. The extreme source of the Beni is the little river La Paz, which rises in the inter-Andean region, a few miles south-east of Lake Titicaca, and flows as a rivulet through the Bolivian city of La Paz. From this point to Reyes the river is a torrent. The principal affluent of the Beni, and one which exceeds it in volume, enters it 120 miles above its mouth, and is known to the Indians along its banks as the Mayutata, but the Peruvians call it the Madre de Dios. Its ramifications drain the slopes of the Andes between 12 degrees and 15 degrees of latitude. It is navigable in the wet season to within 180 miles of Cuzco. Its upper waters are separated by only a short transitable canoe portage of 7 miles in a straight line from those of the Ucayali. The portage on the eastern side terminates at the Cashpajah river 22 miles above its junction with the Manu. For the first 13 miles it is navigable all the year for craft drawing 18 in. of water, but the remaining 9 miles present many obstacles to navigation. At the Manu junction the elevation above sea-level is 1070 feet, the river width 300 feet, depth 8 feet, current 1 1/4 miles per hour. The general direction of the Manu is south-east for 158 miles as far as the Pilcopata river, where under the name of Madre de Dios it continues with a flow of 22,000 cubic metres per minute. Here its elevation is 718 feet above the sea and its width 500 feet. During the above course of 158 miles the Manu receives 135 large and small affluents. Although the inclination of its bed is not great, the obstacles to free navigation are abundant, and consist of enormous trees and masses of tree-trunks which have filled the river during the period of freshets.
From the time it receives the Manu, the Madre de Dios carries its immense volume of waters 485 miles to the Beni over the extremely easy slope of a vast and fertile plain. Its banks are low, its bottom pebbly. A greater part of its course is filled with large and small islands some 63 in number. Its average width is about 1500 feet. Below the mouth of the Tambopata, the flow is estimated at 191,250 cubic metres per minute. The average current is 2 1/2 miles per hour. There are two important rapids and one cataract on the lower 300 miles of the river.
The Peruvian government has sought to open a trade route between the Rio Ucayali and the rich rubber districts of the Mayutata. All of the upper branches of the river Madeira find their way to the falls across the open, almost level Mojos and Beni plains, 90,000 km2 (35,000 square miles) of which are yearly flooded to an average depth of about 3 feet for a period of from three to four months. They rival if they do not exceed in fertility the valley of the Nile, and are the healthiest and most inviting agricultural and grazing region of the basin of the Amazon.