The Javary River or Yavarí River is a 1,184 km tributary

Tributary

A tributary or affluent is a stream or river that flows into a main stem river or a lake. A tributary does not flow directly into a sea or ocean...

 of the Amazon

Amazon River

The Amazon of South America is the second longest river in the world and by far the largest by waterflow with an average discharge greater than the next seven largest rivers combined...

 that forms the boundary between Brazil

Brazil

Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...

 and Peru

Peru

Peru , officially the Republic of Peru , is a country in western South America. It is bordered on the north by Ecuador and Colombia, on the east by Brazil, on the southeast by Bolivia, on the south by Chile, and on the west by the Pacific Ocean....

 for more than 500 miles. It is navigable by canoe

Canoe

A canoe or Canadian canoe is a small narrow boat, typically human-powered, though it may also be powered by sails or small electric or gas motors. Canoes are usually pointed at both bow and stern and are normally open on top, but can be decked over A canoe (North American English) or Canadian...

 for 900 miles from above its mouth to its source in the Ucayali

Ucayali

The Ucayali River arises about north of Lake Titicaca, in the Arequipa region of South America. The Amazon River takes its name close to Nauta city , in the confluence among Ucayali and Marañón rivers....

 highlands, but only 260 were found suitable for steam navigation. The Brazilian Boundary Commission ascended it in 1866 to the junction of the Shino

Shino

-People:*George Shenton , English footballer nicknamed Shino*Shino Correa, a latin musician in Grupo Aguakate*Shino Kakinuma , Japanese actress*Shino Lin , a Taiwanese singer and actress...

 with its Jaquirana

Jaquirana

-See also:*List of municipalities in Rio Grande do Sul...

 branch. The country it traverses in its extremely sinuous course is very level, similar in character to that of the Jurua

Jurua

The Juruá River is a southern affluent river of the Amazon River west of the Purus River, 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...

.

The river is one of the best places to observe Amazonian wildlife, including the Amazon river dolphin and tucuxi

Tucuxi

The Tucuxi , alternately bufeo gris or bufeo negro is a dolphin found in the rivers of the Amazon Basin. The word "tucuxi" is derived from the Tupi language word tuchuchi-ana and has now been adopted as the species' common name...

. There are a number of small private reserves along the river, which arrange wildlife viewing

The town of Benjamin Constant

Benjamin Constant, Amazonas

Benjamin Constant is a town and municipality located in the Brazilian state of Amazonas. Its population was 26,191 and its area is 8,793 km² ....

lies at the mouth of the river, on the Brazilian bank.