Historical range included the Rio Grande and Pecos River systems, Texas, New Mexico, and Mexico; in the Rio Grande, this species occurred from Española, New Mexico, downstream to the Gulf of Mexico; in the Pecos River it occurred from the Rio Grande to Santa Rosa, New Mexico; it also occurred in the lower Rio Chama and the lower Jemez River, tributaries of the Rio Grande in New Mexico (USFWS 2010). It has never been found in any Mexican tributaries to the Rio Grande, despite extensive collection efforts (Edwards et al. 2003). Currently, the species is known to occur only in one reach of the Rio Grande in New Mexico, a 280 km stretch of river that runs from Cochiti Dam to the headwaters of Elephant Butte Reservoir; this includes a small portion of the lower Jemez River, a tributary to the Rio Grande north of Albuquerque (Sublette et al. 1990; Bestgen and Platania 1991; USFWS 1994, 1999, 2007; 2010; Bestgen and Propst 1996; Dudley et al. 2005). An estimated 90-95 percent of the population is believed to be in the 96 km portion of the Rio Grande downstream of the San Acacia Dam (Ikenson 2002).

Nonessential experimental population: Rio Grande, from Little Box Canyon (approximately 10.4 river miles downstream of Fort Quitman, Texas) to Amistad Dam, Texas; and Pecos River, from its confluence with Independence Creek to its confluence with the Rio Grande, Texas.