Pecan Bayou originates in northwestern Callahan County and eastern Taylor County on the Callahan Divide, flowing southeast through Coleman and Brown Counties before joining the Colorado River in northern Mills County, approximately eight miles west of Goldthwaite. This 100-mile waterway represents the westernmost "bayou" in the United States and serves as one of five major tributaries to the Texas Colorado River.

The river's character transitions dramatically along its course. In Callahan County, two main branches—the North Prong and South Prong—merge in the south-central portion of the county after the North Prong passes through Lake Clyde. The combined flow continues through Coleman County, where it receives contributions from multiple creeks before entering Brown County. Here, the river is impounded to form Lake Brownwood, a 7,300-acre reservoir constructed between 1930 and 1933. Below the dam, Pecan Bayou flows through the cities of Brownwood and Early as a slow-moving, controlled waterway before continuing into Mills County.

Paddling opportunities exist primarily below Lake Brownwood in Brown County. The Pecan Bayou Paddling Trail offers a 3.2 to 7.2-mile experience launching from Fabis Primitive Park, accessible via FM 2125 north of Brownwood. This peaceful stretch features slow-moving water suitable for all skill levels, making it ideal for beginners and families. Paddlers can navigate upstream and back (3.2 miles) or downstream to the dam and return (4 miles), with float times ranging from one to three hours depending on water levels and wind conditions. The trail passes through an old pecan orchard where hundred-year-old pecan trees line the banks.

The river's flow is controlled by Lake Brownwood's dam and influenced by rainfall, creating variable conditions. Water quality can be temporarily affected by rainfall runoff.

The bayou supports populations of largemouth bass, white bass, white crappie, channel catfish, blue catfish, and flathead catfish. Wildlife viewing opportunities include Eastern Bluebirds, Great Horned Owls, Eastern Screech Owls, Barred Owls, Golden-fronted and Ladder-backed Woodpeckers, kingfishers, herons, and egrets. Winter months bring Northern Pintails, Mallards, and Blue-winged Teal.

Access points include Fabis Primitive Park and Riverside Park in Brown County, both located along FM 2125 below Brownwood Reservoir. The paddling trail is approximately 70 miles southeast of Abilene and provides easy access from Brownwood.

Pecan Bayou has supported human settlement for centuries, with Tonkawa and Comanche peoples gathering pecans, wild plums, and acorns along its banks. The river is classified as navigable under Texas law, permitting public use of the streambed while requiring respect for adjacent private property. Paddlers should remain aware that the bayou is readily influenced by rainfall runoff, which may create temporary high flows and undesirable water conditions.