The Pará River is the southern arm of the mouth of the Amazon River

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...

. It flows round the west and south of the island of Marajó

Marajó

Marajó is an island located at the mouth of the Amazon River in Brazil. It is part of the state of Pará.- Geography :With a land area of 40,100 km² , which compares to the size of Switzerland, it is the largest island to be completely surrounded by freshwater in the world...

. It takes some water from the main Amazon, however much of its power comes from the Tocantins River

Tocantins River

The Tocantins is a river in Brazil, the central fluvial artery of the country. In the Tupi language, its name means "toucan's beak" . It runs from south to north for about 2,640 km. It is not really a branch of the Amazon River, although usually so considered, since its waters flow into the...

 flowing from the south. The state capital of Pará

Pará

Pará is a state in the north of Brazil. It borders the Brazilian states of Amapá, Maranhão, Tocantins, Mato Grosso, Amazonas and Roraima. To the northwest it also borders Guyana and Suriname, and to the northeast it borders the Atlantic Ocean. The capital is Belém.Pará is the most populous state...

, Belém

Belém

Belém is a Brazilian city, the capital and largest city of state of Pará, in the country's north region. It is the entrance gate to the Amazon with a busy port, airport and bus/coach station...

, is located on the south bank of the river. It is approximately 40 miles long.