The Sabine River rises in three main branches-the Cowleech Fork, the Caddo Fork, and the South Fork. A fourth branch known as the Lake Fork of the Sabine or Lake Fork Creek, joins the main stream forty miles downstream from the junction of the other three branches. The Cowleech Branch rises in northwestern Hunt County and flows southeast for thirty-five miles to the extreme southwestern corner of the county, where its confluence with the Caddo Fork and the South Fork forms the Sabine River proper (at 32°48' N, 95°55' W). The former juncture is now inundated by Lake Tawakoni, constructed in 1958. The Caddo Fork rises in two tributary forks, the East Caddo Fork and the West Caddo Fork, in northwestern Hunt County. These streams unite in the southern part of the county to form the Caddo Fork, which flows southeast to its junction with the South Fork and the Cowleech Fork. The South Fork rises in the southwestern corner of Hunt County and flows east for eighteen miles to join the Caddo Fork and Cowleech Fork. From this point the Sabine River runs southeast, forming the boundary lines between Rains and Van Zandt, Van Zandt and Wood, Wood and Smith, and Smith and Upshur counties. After crossing most of Gregg County, the river forms portions of the county lines between Gregg and Harrison, Harrison and Rusk, and Harrison and Panola counties before it bends more sharply across Panola County. At the thirty-second parallel in the southeastern corner of Panola County the Sabine becomes the state boundary between Texas and Louisiana, and thus the eastern boundary of Shelby, Sabine, Newton, Orange, and Jefferson counties. The river empties into Sabine Lake (at 29°59' N, 93°47' W), which is formed by the confluence of the Neches and the Sabine rivers; the lake is drained by Sabine Pass into the Gulf of Mexico.
The Sabine flows for 555 miles. Its total drainage basin area is 9,756 square miles, of which 7,426 is in Texas and the remainder in Louisiana. Unlike most Texas rivers, the Sabine is entirely in an area of abundant rainfall. Average annual precipitation is between thirty-seven inches at its source and fifty inches at its mouth. Also it flows through forested sandy country adaptable to the conservation of runoff and is fed by many flowing tributaries and springs. It has, therefore, a remarkably strong flow for its length, and it discharges the largest volume of water at its mouth of all Texas rivers. Average runoff within 97 percent of the Sabine River basin during the 1941–67 period was about 640 acre-feet per square mile. Two large reservoirs have been constructed on the Sabine: Lake Tawakoni, at the junction of the South and Cowleech forks, now in Hunt, Rains, and Van Zandt counties; and Toledo Bend Reservoir, on the Texas and Louisiana border. The Sabine River basin is characterized by flat slopes and wide, timbered floodplains. High rainfall rates produce frequent flooding of low-lying areas, and large floods occur, on the average, every five years. Floods generally rise and fall slowly, although flash floods occasionally occur in the basin. During flood the lowest part of the basin usually remains inundated for many days, and sometimes for several weeks. The extreme southern portion of the river is subject to hurricane flooding. In its upper reaches the river traverses rolling terrain with soils of deep sandy loams, loamy sands, and sand. Loblolly, longleaf, and shortleaf pine, post, southern, red and white oak, and flowering dogwoods grow throughout the region. Cottonwood, cypress, hackberry, pecan, blackgum, hickory, and blackjack oak are scattered throughout the area. A variety of native grasses is also found, including little and big bluestem, Indian grass, switch grass, grama grass, and Virginia wild rye. In its lower reaches, the Sabine flows through generally flat terrain with a substrate composed of sand, gravel, and mud. Vegetation in this region consists largely of water-tolerant hardwoods, conifers, and grasses.
The Sabine River basin has long been the site of human habitation. Archeological excavations have discovered evidence of all stages of southeastern Indian development, beginning with the 12,000-year-old Clovis culture. Indian development reached its peak after the arrival of the Caddos about A.D. 780. The early Caddoan Period, which lasted until about 1260, saw the construction of large mounds, the southwesternmost example of the Mississippian mound-building culture. In the Late Caddo Period, many of the mound sites were abandoned, but numerous sites show a continuing Caddoan presence in the area until the beginning of the historical era.
When the first Europeans entered the area in the sixteenth century, they found various groups of Caddos living along the stream. The name Sabine (Río de Sabinas) comes from the Spanish word for cypress and refers to the great growth of cypress trees along the lower river. The stream was evidently named by Domingo Ramón in 1716, for it was designated Río de Sabinas on a map of 1721 giving the route of the expedition led by the Marqués de Aguayo. The Spanish considered territory west of the Sabine, and some territory to the east, to be part of the Spanish province of Texas. After the acquisition of Louisiana by Spain, Spanish officials debated about whether the Sabine should form the eastern boundary of Texas. The capital of the province of Texas, however, was Los Adaes, on the east side of the river near the present site of Robeline, Louisiana. French traders operated along the Sabine, and both nations claimed the area. An examination of old Spanish maps shows that up to the end of the eighteenth century little was known about the topography of East Texas. Some Spanish maps labeled the Sabine Río de los Adais (Adaes, Adiais, or Adays); others, failing to show Sabine Lake, pictured both the Sabine and the Neches flowing directly and independently into the Gulf of Mexico, or depicted the two rivers joining to form one river before entering the Gulf; yet other maps showed only one river. Some mapmakers referred to the Sabine as the Río Mexicano; others used this designation for the Neches. José Antonio Pichardo, who made a close study of the Louisiana-Texas boundary in the first decade of the nineteenth century, reported all of this past confusion, pointing out at the same time that the fixed names of the two streams-Neches or Río de Nievas for the western river and Río de Sabinas for the eastern-had been well established for years and that, when the name Río Mexicano was used, it was only properly applied to the Neches.
After the purchase of Louisiana by the United States, the indefiniteness of the western boundary led Gen. James Wilkinson and Lt. Col. Simón de Herrera on November 6, 1806, to enter into an agreement establishing a Neutral Ground, which extended from the Arroyo Hondo on the east to the Sabine on the west. The Adams-Onís Treaty (1819) established the western boundary of Louisiana and the eastern boundary of Texas as beginning at the Gulf and extending up the Sabine to the thirty-second parallel. Spanish delay in ratification of the treaty and Mexican independence (1821) put the boundary again in controversy. The United States for a time claimed that the names of the Neches and Sabine rivers had been reversed (see NECHES RIVER BOUNDARY CLAIM), but no definite settlement was made. On December 19, 1836, the Congress of the Republic of Texas set forth the northern and eastern boundaries of the republic as stipulated in the Adams-Onís Treaty, and the United States dropped the claim to the area between the Sabine and the Neches. Despite the attempts of the Spanish to colonize the area, large numbers of Europeans did not enter the Sabine basin until the 1820s, when Americans from the southern United States began to settle there. When Mexican general Manuel de Mier y Terán was sent to the region in 1828 to report on conditions, he found that the ratio of Americans to Mexicans was nearly ten to one.
In the early days of the republic the Sabine furnished transportation facilities for lumber and cotton from Southeast Texas. Great logs cut from the pine forest were lashed together to make rafts, which were then floated downstream. Although more difficult to manipulate, flatboats loaded with cotton and other products were also transported. Once the boats reached Sabine Bay, their cargoes were loaded on larger ships for transport to New Orleans, Galveston, and other ports. The booming river trade on the Sabine and Neches contributed to the rise of Port Arthur and Orange. The first steamships began to ply the river in the late 1840s. Noted riverboats that served the Neches-Sabine basin included the Neches Bell, Pearl Rivers, Florida, Laura, Star, Katy, Frankie, Extra, and Maude Howell. Although by the 1870s and 1880s railroads had begun to replace steamboats as the most important medium for transporting trade goods, the riverboats continued to navigate the waters of the Neches until 1900. Several of the last of the large steamers, including the Neches Belle, the Extra, and the Maude Howell, sank on the river between 1890 and 1900.
During the late nineteenth and early twentieth centuries the middle Sabine River basin was the site of intensive logging operations, and numerous sawmills were built along the banks of the river and its tributaries. Downstream, the irrigation projects were built during the early 1900s. After the Spindletop oilfield boom of 1901, the Sabine basin also became the site of large-scale oil exploration. The growth of the oil industry led to the development of the Beaumont-Port Arthur-Orange metropolitan area as a major site for oil refining, processing, and shipping. As a consequence of these developments, the once clean waters of the Sabine became increasingly polluted. Decaying vegetation produced natural pollution. Runoff from fields added fertilizers, pesticides, and herbicides. Oil refineries and chemical plants discharged ammonia, phenol, sulfides, heavy metals such as zinc and lead, and other chemicals into the river. Straightening and deepening of the lower reaches of the river to improve navigation allowed salt water to back up into the estuary. Upstream diversions resulted in the lower reach of the river being frequently composed of a large percentage of treated municipal and industrial effluent. In recent years, however, efforts have been made to clean up the stream. An areawide water-quality management plan was adopted for the Beaumont-Port Arthur-Orange metropolitan area. But in the early 1990s the pollution problem continued, especially in the river's lower reaches. Management of the river and its watershed is overseen by the Sabine River Authority of Texas. In 1980 the population of the Sabine River basin was reported at 407,300. Longview is the largest city in the basin; other large cities include Marshall, Orange, and Greenville.