Rio Pacaás Novos, Rondônia, Brazil

Sponsored by

Brazil, Rondônia, Guajará-Mirim

The Pacaás Novos National Park, which was created in 1979. The park takes its name from the Pacaás Novos River, which rises in the Pacaás Novos mountains in the west of the park and flows southwest via the Rio Pacaás Novos Extractive Reserve to join the Mamoré River.

The accelerated agricultural expansion made it essential to protect and preserve this broad and diverse region’s ecosystems, like the transition between the Cerrado and the Amazon rainforest and the many endangered species of flora and fauna. The most notable parts of the park include: Complete Protection Conservation (14.3% of the area) and Indigenous Lands (29%). Open Rain Forest account for 38% of the total area while dense rainforests for 5%, savannas for 27% and Cerrado (an area between savanna and rainforest) for 30%. The park has a total area of 764.801 ha and altitudes ranges from 100 to 1.230m (330 to 4,040ft).

Submitted by
Konstantinos Gazos
Approved by
Roberto E. Reis & Flávio Lima
-11.2359438, -64.4750900
Geographical region
South America
Drainage Basin
Rio Amazonas
River catchment
Rio Madeira
Water body type
Water body name
Pacaás Novos
Water body part
Water body course
Middle course
Water body: tributary of
Tributary name

Water Chemistry

Water information

Water type
Fresh water
Water color
Black water
Water transparency
Concentration of sediments
Water temperature
25 °C
Water flow/curent

Chemical parameters

5 mg/l
3 mg/l
Dissolved Oxygen

Substrate in nature

Stone form
Submerged terrestrial vegetation

Aquatic Biotope

Date of collecting
Collecting area
Water depth
Air temperature


Affected by human activity
Affected by human activity
Surrounding area

The vegetation is vastly diverse. In higher altitudes, extensive areas of savannas (cerrado) can be observed while in the valleys and slopes typical Amazonian forests. There are also large areas of contact between the savannas and the rainforest.

The National Park brings together a drainage network that has a dendritic and radial pattern. Rivers and streams form rapids and waterfalls influenced by the unique geomorphology of the region. This network encompasses the three main hydrographic basins of the state: Guaporé, Mamoré and Madeira, represented by Rio Pacaás Novos (tributary of the Rio Mamoré).

The fauna consists of species of both Amazon rainforests and Cerrado, many of which are dangered, such as Leopardus wiedii. The National Park, which still does not have a visitation structure, is home to the Tracoá mountain range, where the highest point ofthe state is, the Tracoá peak, with 1.230m.

Underwater landscape

The rivers have a sandy bed, for the most part, and follow the pluvial regime characteristic of the Amazon. Some rivers with rocky bottoms and steep slopes form waterfalls. In parts where the flow is reduced dense semiaquatic vegetation can be seen.

A lot of submerged terrestrial vegetation is also present. Driftwood and fallen branches, seeds and pods are observed near the bays of the river. While the rivers are mainly blackwater, visibility ranges from low to high depending on the current and the sediment accumulation.


  • Apistogramma trifasciata (Cichlidae) – 6
  • Aphyocharax rathbuni (Characidae) – 60
  • Mesonauta festivus (Cichlidae) – 4
  • Nannostomus trifasciatus (Lebiasinidae) – 12

Wetland plans:

  • Hydrocotyle leucocephala (Apiaceae )

Aquatic plants:

  • Pontederia crassipes (Pontederiaceae)
Threats to ecology

On the Jamari River the Samuel Hydroelectric Power Plant was built, the main electricity source of the state.
Almost all of the reservoir area was covered in tropical forest before the dam was built. Environmental studies were not required by law at the time of construction. It has been noted that the region was undergoing rapid deforestation, when the dam was built, so the area now covered by the dam would probably otherwise be covered by degraded cattle pasture, as is the case in neighbouring areas. However, an exception to the Brazilian law prohibiting export of logs was created for Samuel, and this caused a boom in illegal logging throughout the western Amazon basin.

Accorrding to Fearnside 2004, the dam emits more greenhouse gas than an oil-fuelled power plant with the same capacity would emit. The reservoir methylated mercury present in the soil, contaminating fish and crustaceans.

Fish populations were studied before and after the dam was built. They showed a drop in diversity, but an increase in the populations of species that included Cichla sp. (tucunare), Schizodon fasciatus (aracu comum), Hypophthalmus marginatus (mapará) and Serrasalmus rhombeus (piranha preta).

The reservoir is now used intensively for fishing, which in the past had been confined to the mouth of the river, causing concerns about sustainability. Forest fires are as well a constant threat.

Riparian zone

Trees near the aquatic habitat
Many -


Comment by the expert

Roberto E. Reis: Good research on the habitat and surroundings. Fair list of species.

Flavio Lima: Although the participant cited several published sources, none of them realy describes the aquatic habitats of the specific biotope he attempted to recreate.