The Atrato River is a river of northwestern Colombia. It rises in the slopes of the Western Cordillera and flows almost due north to the Gulf of Urabá, where it forms a large, swampy delta. Its course crosses the Chocó Department, forming that department's border with neighboring Antioquia in two places. Its total length is about 650 km, and it is navigable as f…The Atrato River is a river of northwestern Colombia. It rises in the slopes of the Western Cordillera and flows almost due north to the Gulf of Urabá, where it forms a large, swampy delta. Its course crosses the Chocó Department, forming that department's border with neighboring Antioquia in two places. Its total length is about 650 km, and it is navigable as far as Quibdó, the capital of the department.