Chapter 24—Rivers of the Northern Pacific
The Pacific slope basins of the Northwest Tropical Andes—from Colombia’s Punta Ardita to Ecuador’s southern Pacific coast—span steep gradients from high‑elevation páramo to rainforest and estuarine systems. These short, steep rivers host exceptional biodiversity and endemism, including threatened reptiles, amphibians and birds. While northern Colombian basins remain relatively intact, gold mining and mercury pollution pose growing risks. In Ecuador, centuries of agricultural expansion and limited wastewater treatment have severely degraded water quality, especially near major cities. This synthesis highlights the ecological richness, environmental pressures and knowledge gaps shaping freshwater ecosystems across this dynamic Andean-Pacific region.
Subject Tags
- Rivers
- Watersheds
- Biodiversity
Abstract
The Pacific slope of South America’s Northwest Tropical Andes region encompasses the area from Cape Punta Ardita in Colombia (7°N) to the southern Pacific coast of Ecuador (3°S). The volcanic activity in this part of the Andes is one of the most important features that contributes to a myriad of soils, vegetation and ecosystems found in this drainage. Rivers of the Northwest Pacific are relatively short (180 to 385 km) and cover high elevation ranges, up to 6263 m a.s.l. in short distances. The basins have páramo ecosystems in the upper parts, followed by montane, rainforest and estuarine systems in the lower parts. The San Juan is the largest river by water volume in the whole South American Pacific. The diversity and endemism of fish and invertebrates in these basins are high with several endangered reptiles, amphibians and bird species. There is limited information available on the biodiversity and ecological status of aquatic plants, algae and other microorganisms at the basin level. Basins in the North Pacific of Colombia are small and well preserved with more than 50% of the natural vegetation still present due to the complex topography and low access. However, gold mining and mercury pollution are a concern in these basins. Comparatively, most basins in the Pacific of Ecuador are larger and have been impacted by human activities since the 1800s, with agricultural production contributing 60% of the GDP. Naturally, stream water in these basins has low nutrient and major anion concentrations. The low degree of wastewater treatment contributed to the severe degradation of rivers, especially around major cities like Quito and Guayaquil, which are located inside the Esmeraldas and Guayas basins in this versant.
Citation
Ríos-Touma, B., Longo, M., Villamarín, C., Carvajal-Escobar, Y., Cantera-Kintz, J., Rosero-López, D., ... & Mojica, J. I. (2025). Rivers of the Northern Pacific. In Rivers of South America (pp. 933-983). Elsevier. https://doi.org/10.1016/B978-0-12-823429-7.00005-7
TNC Authors
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Pedro Jiménez-Prado
Freshwater Conservation Scientist, Ecuador
The Nature Conservancy
Email: pedro.jimenez@tnc.org