The Trombetas is a river

River

A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...

 on the northern side 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...

. Its confluence

Confluence

Confluence, in geography, describes the meeting of two or more bodies of water.Confluence may also refer to:* Confluence , a property of term rewriting systems...

 with the Amazon is just north of the town of Óbidos, Pará

Óbidos, Pará

Óbidos is a town in Pará, Brazil located at the narrowest and swiftest part of the Amazon River. Its an old town founded in 1697, and located between Santarém and Oriximiná. The town is the seat of the Diocese of Óbidos. The town was named after Óbidos, Portugal.-Further...

 in 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...

. It has its sources in the Guyana highlands, but its long course is frequently interrupted by violent currents

Current (stream)

A current, in a river or stream, is the flow of water influenced by gravity as the water moves downhill to reduce its potential energy. The current varies spatially as well as temporally within the stream, dependent upon the flow volume of water, stream gradient, and channel geometrics...

, rocky barriers, and rapid

Rapid

A rapid is a section of a river where the river bed has a relatively steep gradient causing an increase in water velocity and turbulence. A rapid is a hydrological feature between a run and a cascade. A rapid is characterised by the river becoming shallower and having some rocks exposed above the...

s. The inferior zone of the river, as far up as the first fall, the Porteira, has but little broken water and is low and swamp

Swamp

A swamp is a wetland with some flooding of large areas of land by shallow bodies of water. A swamp generally has a large number of hammocks, or dry-land protrusions, covered by aquatic vegetation, or vegetation that tolerates periodical inundation. The two main types of swamp are "true" or swamp...

y; but above the long series of cataracts and rapids the character and aspect of the valley

Valley

In geology, a valley or dale is a depression with predominant extent in one direction. A very deep river valley may be called a canyon or gorge.The terms U-shaped and V-shaped are descriptive terms of geography to characterize the form of valleys...

 completely change, and the climate

Climate

Climate encompasses the statistics of temperature, humidity, atmospheric pressure, wind, rainfall, atmospheric particle count and other meteorological elemental measurements in a given region over long periods...

 is much better. The river is navigable

Navigability

A body of water, such as a river, canal or lake, is navigable if it is deep, wide and slow enough for a vessel to pass. Preferably there are few obstructions such as rocks or trees to avoid. Bridges must have sufficient clearance. High water speed may make a channel unnavigable. Waters may be...

for 135 miles above its mouth.