Aquarist Atlas
Water character

Clearwater river

Clearwater rivers are the third of the classic Amazonian water types: greenish-transparent rivers draining old, deeply weathered shield rock, low in sediment and low in dissolved minerals at once. The Tapajós and Xingu are the type cases; in this atlas the label also covers river basins whose mainstem runs broadly clear, the Orinoco chief among them.

A clearwater river drains ancient rock — the Guiana and Brazilian shields and their kin — that erosion finished with long ago. With little silt to carry and little mineral left to dissolve, the water runs transparent with a green or blue cast, visibility measured in metres, pH mildly acidic to neutral. In chemistry it sits between the two extremes: cleaner than whitewater, less acid and less empty than blackwater.

The typology is a spectrum, and big basins braid the types together. The Orinoco carries tea-black tributaries off the Guiana Shield into a broadly clear mainstem, and its measured values span both worlds — blackwater reaches under 20 µS/cm against a mainstem around 50–100. The atlas types each river basin by its dominant character, and several broad regional systems (Madagascar's rivers, India & Sri Lanka, the Hormozgan drainages) sit under this label as generally clear-running river regions; each water's own page carries its measured values, which always outrank the label.

Clearwater habitat is sunlit habitat, and its fish behave accordingly: eartheaters sifting open sand flats in full view, pike cichlids holding against rock, fish that live by sight in a way no blackwater shade-dweller does. Light, as much as chemistry, is what this water type means.

Waters of this character in the atlas (12)

AsiaCoastal India & Sri Lanka →3 native (Etroplus / Pseudetroplus) cichlid speciesPersian GulfHormozgan Coastal Rivers →2 (endemic Iranocichla) cichlid speciesLevantJordan River & Lake Hula →~5 native cichlid speciesNorth AmericaLower Rio Grande →1 native (Herichthys cyanoguttatus) + introduced cichlid speciesMadagascarMadagascar's Rivers & Lakes →~37 (≈29 endemic) cichlid speciesCentral AfricaThe Congo Basin →~80–100+ (basin); 20+ endemic to the lower rapids cichlid speciesWest AfricaThe Niger & Volta →~30–40 cichlid speciesAfricaThe Nile System →~10–15 cichlid speciesSouth AmericaThe Orinoco Basin →~90+ cichlid speciesSouth AmericaThe Paraná–La Plata →~25–40 cichlid speciesSouth AmericaThe Río Uruguay (middle & lower) →~10–15 cichlid speciesSouthern AfricaThe Zambezi & Okavango →~30+ cichlid species

Sources

  1. Physicochemical characterization of white, black and clearwater rivers (Pan-American Journal of Aquatic Sciences): pH and conductivity by water type
  2. Chemistry of different Amazonian water types for river classification: a preliminary review (Ríos-Villamizar et al., WIT Trans. Ecol. Environ. 178, 2014)
  3. The freshwater habitats, fishes, and fisheries of the Orinoco River basin (Rodríguez, Winemiller, Lewis & Taphorn, Aquatic Ecosystem Health & Management, 2007) — open-access PDF
How to cite

Aquarist Atlas (2026). Clearwater river — water character. Aquarist Atlas. https://www.aquaristatlas.com/water/type/clearwater-river/