The Trinity River is a 710-mile (1,140 km) river, the longest with a watershed entirely within the U.S. state of Texas. It rises in extreme northern Texas, a few miles south of the Red River. The headwaters are separated by the high bluffs on the southern side of the Red River. Indigenous peoples call the northern sections Arkikosa and the parts closer to the coast Daycoa. French explorer Robert Cavelier de La Salle, in 1687, named it Riviere des canoës ("River of Canoes"). In 1690 Spanish explorer Alonso de León named the river "La Santísima Trinidad" ("the Most Holy Trinity"), in the Spanish Catholic practice of memorializing places by religious references. From Wikipedia