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#10351 Forest stream, Puca Urco area, Rio Nanay affluent, Peru

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Peru, Loreto, Mariscal Ramón Castilla Province (Pebas area)

The Rio Nanay is a left-bank tributary of the Amazon River, joining it near the city of Iquitos, Peru. It flows through tropical rainforest and is fed by numerous smaller tributaries and forest streams.

One of the most interesting areas is around Puca Urco, where many small tributaries converge. The steep, undercut banks of these forest streams create a striking landscape. Unlike gently sloping shores that gradually merge into sandy substrates, these streams are characterised by sharply eroded banks that seem to plunge directly into the water. Parts of the banks, together with the surrounding riparian vegetation, are often seasonally flooded, creating a unique and dynamic habitat.

Submitted by
Jacek Pietrzak
GPS
-3.2681320, -74.3097839
Geographical region
South America
Drainage Basin
Rio Amazonas
River catchment
Rio Nanay
Water body type
Stream
Water body name
Forest stream near Puca Urco
Water body part
Flood plain
Water body course
Middle course
Water body: tributary of
River
Tributary name
Rio Nanay

Videos above and below water


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Water Chemistry

Water information

Water type
Freshwater
Water color
Mixed water
Water transparency
High
Concentration of sediments
Medium
Water temperature
26.5 °C
Water flow/curent
Slow

Chemical parameters

pH
6.0
Conductivity
24
GH
2 mg/l
dGH
KH
1 mg/l
dKH
Dissolved Oxygen
5 %

Substrate in nature

Sand
Beige
Pebble/Gravel
None
Stone
None
Stone form
Silt/Mud
Brown
Leaves
Many
Driftwood
Many
Submerged terrestrial vegetation
Yes

Aquatic Biotope

Date of collecting
Collecting area
River bank
Water depth
0,5m
Air temperature
Sunlight
Full sun

Environment

Environment
Affected by human activity
Affected by human activity
Agriculture
Agriculture
Little
Surrounding area

Puca Urco is a small settlement in the Loreto Region of the Peruvian Amazon, located near the Nanay and Pintuyacu rivers. The region is currently facing a serious environmental threat caused by illegal gold mining using dredges, which severely damages local ecosystems.

Mercury is used during the extraction process, contaminating both the water and the fish. As mercury enters the food chain (fish → people), it increases the risk of neurological disorders and mercury poisoning while also reducing the quality of drinking water for the city of Iquitos, located downstream.

Terrestrial vegetation

  • Ceiba pentandra (Malvaceae)
  • Dipteryx odorata (Fabaceae)
  • Mauritia flexuosa (Arecaceae)
  • Euterpe precatoria (Arecaceae)
Underwater landscape

During the rainy season, the river floods the surrounding forest. Tree roots, branches, and the trunks of fallen trees become submerged. A thick layer of leaf litter covers the bottom, while large aquatic plants are almost absent. The result is a submerged forest that resembles an underwater jungle.

The riverbed consists mainly of white or brown sand, with no rocks or stones. In some areas, a layer of silt and decomposing leaves accumulates on the bottom. These conditions provide habitat for small schooling fish (mainly characins), dwarf cichlids, and small bottom-dwelling catfish. In some places, human activities have disturbed the substrate, making it more unstable.

Fish

  • Apistogramma agassizii (Cichlidae) – 4
  • Nannostomus marginatus (Lebiasinidae) – 20
  • Otocinclus affinis (Loricariidae) – 11

Wetland plant

  • Helanthium tenellum (Alismataceae) – 100

Aquatic plant

  • Hydrocotyle leucocephala (Araliaceae) – 100
Threats to ecology

The Rio Nanay region near Puca Urco (Loreto, Peruvian Amazon) is of exceptional ecological importance, as it forms part of one of the world’s most fragile and biologically diverse ecosystems. It belongs to the Amazon Basin, the largest river system on Earth, linking seasonally flooded forests with the Amazon’s main ecological corridor. The river acts as a lifeline for the entire region, and environmental changes here can affect large parts of the Amazon. It was this remarkable ecosystem that inspired me to recreate the region in my aquarium.

Riparian zone

Trees near the aquatic habitat
Many -

Bibliography

Sitography

→ UNAP