Entirely within Texas, this Colorado River has its origins near Lamesa and empties into the Gulf of Mexico in Matagorda County below Bay City. Near its start, it forms Lake Thomas, then near Robert Lee it fills E.V. Spence Reservoir. It fills O.H. Ivie Reservoir near Ballinger and forms Lake Buchanan near Buchanan Dam before passing through Austin and forming Lake Walter E. Long. It then makes a gentle southeast curve to its outlet.