The Tapajós, a Brazilian river running through a humid, hot and unhealthy valley, pours into the Amazon River 500 miles above Pará and is about 1200 miles long.

It rises on the lofty Brazilian plateau near Diamantino in 14 degrees 25' southers latitude. Near this place a number of streams unite to form the river Arinos , which at latitude 10 degrees 25' joins the Juruena to form the Alto Tapajós , so called as low down as the Rio Manoel , entering from the east.

Thence to Santarém the stream is known as the Tapajós. The lower Arinos , the Alto Tapajos and the Tapajos to the last rapid, the Maranhão Grande , is a continuous series of formidable cataracts and rapids; but from the Maranhao Grande to its mouth, about 188 miles, the river can be navigated by large vessels.

For its last 100 miles it is from 4 to 9 miles wide and much of it very deep. The valley of the Tapajós is bordered on both sides by bluffs. They are from 300 to 400 foot high along the lower river; but, a few miles above Santarém, they retire from the eastern side and only approach the Amazon flood-plain some miles below Santarém.

The Tapajós is named after the Tapajós Indians , a tribe of Native Americans from Santarém known for some unusual practices.