Agua Negra Creek rises sixteen miles south of Lytle in northern Atascosa County (at 29°09' N, 98°39' W) and runs southeast for eight miles to its mouth on Palo Alto Creek, three miles northwest of Poteet (at 29°03' N, 98°37' W). The terrain at the source is flat to rolling and exhibits local escarpments; there deep, fine sandy loam supports brush and grasses. Towards the mouth, locally active blowout areas replace the escarpments, and clay and sandy loam supports bunch grasses. The land is predominantly forested. The creek was named for a spring that fed it with water darkened by iron sediment or oil. The spring has been dry since 1915.