Ayish Bayou rises about seven miles north of San Augustine in northern San Augustine County, near the Shelby county line (at 31°37' N, 94°06' W). Before the development of Sam Rayburn Reservoir, the stream ran southeast for forty-seven miles through central San Augustine County before disemboguing into the Angelina River in northern Jasper County (at 31°04' N, 94°05' W). With the impoundment of the reservoir, the lower reaches of the creek were inundated. The banks of the stream are heavily wooded in places with pine and hardwood trees; the terrain is nearly level to moderately steep and surfaced by loamy and clayey soils that support farming and lumbering. The stream's name is probably a variant of that of the Ais Indians, who lived in the area. About 1820 the bayou became the site of the earliest settlements in what later became San Augustine County.