Productive areas include the deep pools immediately downstream of major riffles and runs, where dorado lie in wait for prey. The confluence of Río Viejo with smaller tributaries often creates nutrient-rich seams that hold concentrations of fish. Extensive sandbars and shallow flats, particularly in the lower sections, are prime areas for sight-fishing to cruising pacú. Undercut banks with overhanging vegetation provide excellent cover for large dorado and catfish.