River is the next great southern affluent of the Amazon river
west of the Purus
, sharing with this the
bottom of the immense inland Amazon depression, and having all the characteristics of the Purus as regards curvature, sluggishness and general features of the low, half-flooded forest country it traverses. It rises among the Ucayali
highlands, and is navigable and unobstructed for a distance of 1133 miles (1823 km) above its junction with the Amazon. It has a total length of approximately 1500 miles (2414 km), and is one of the longest tributaries of the Amazon.