Açude Castanhão, officially known as Açude Público Padre Cícero, is a massive freshwater reservoir impounding the Rio Jaguaribe in the state of Ceará, northeastern Brazil. Constructed between 1995 and 2002 and flooded in 2004, it stands as the largest multiple-use public reservoir in Brazil and the largest dam built on an intermittent river in the country. Located near the municipality of Jaguaribara — approximately 307 kilometers from the state capital of Fortaleza — the reservoir spans portions of four municipalities: Jaguaribara, Alto Santo, Jaguaretama, and Jaguaribe. With a total storage capacity of 6.7 billion cubic meters, Castanhão alone accounts for roughly 37% of the entire storage capacity of Ceará's approximately 8,000 reservoirs, making it a truly extraordinary body of water. The reservoir stretches approximately 48 kilometers in length and 3.5 kilometers in width, covering a surface area of around 36,000 hectares (89,000 acres). It serves multiple purposes including drinking water supply, irrigated agriculture, aquaculture, sport and subsistence fishing, and nautical recreation.