Rio Caldeirão is a notable tributary flowing through the semi-arid sertão of Piauí, Brazil, where it feeds into the Dos Matos River system before ultimately connecting to the broader Parnaíba River basin, which drains eastward to the Atlantic Ocean. The river is defined by its seasonal flow patterns, heavily influenced by the region's intermittent rainfall cycles typical of northeastern Brazil's semi-arid climate. The most significant feature along the river is the historic Açude Caldeirão — the Caldeirão Dam — a landmark structure constructed between 1937 and 1945 by Brazil's National Department of Drought Works (DNOCS). Built originally to combat the devastating droughts that periodically strike the region, the dam and its impoundment have become the focal point of fishing, irrigation, and regional tourism in the area. Today, the reservoir supports recreational activities including boating and watersports, and has long been managed with pisciculture — the deliberate stocking and cultivation of multiple fish species — making it a productive destination for anglers in Piauí's interior.