Water quality characteristics and emerging organic pollutants were sampled along the San Pedro-Guayllabamba-Esmeraldas River and its main water pollution streams in the summer of 2013. The annual flow rate of the stream is 22 000 Mm(3) y(-1) and it collects the wastewater of Quito-Ecuador in the Andes and supplies drinking water to the city of Esmeraldas near the Pacific Ocean. The most persistent emerging pollutants were carbamazepine and acesulfame, which were found to be stable along the San Pedro-Guayllabamba-Esmeraldas River, whereas the concentration of most other organic emerging pollutants, such as caffeine, sulfamethoxazole, venlafaxine, O-desmethylvenlafaxine, and steroidal estrogens, was degraded to a large extent along the 300 km flow. The mass rate of the sum of cocaine and benzoylecgonine, its metabolite, was increased along the stream, which may be attributed to coca plantations and wild coca trees. This raises the possibility of using river monitoring as an indirect way to learn about changes in coca plantations in their watersheds. Several organic emerging pollutants, such as venlafaxine, carbamazepine, sulphamethoxazole, and benzoylecgonine, survived even the filtration treatment at the Esmeraldas drinking water system, though all except for benzoylecgonine are found below 20 ng L(-1), and are therefore not likely to cause adverse health effects. The research provides a way to compare drug consumption in a major Latin American city (Quito) and shows that the consumption of most sampled drugs (carbamazepine, venlafaxine, O-desmethylvenlafaxine, sulphamethoxazole, ethinylestradiol) was below their average consumption level in Europe, Israel, and North America.