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The Mexican freshwater fish that are at risk or extinct are listed by family, state, basin/region, and causes of risk. Of the 506 known species, 168 are at some level of risk, and 25 are believed to be extinct. States with the most reports are: Chihuahua ( 46); Coahuila ( 35); Nuevo Leon ( 20); Sonora ( 19); Durango ( 18); and Tamaulipas ( 15). With the exception of Sonora, these states are largely located in the Rio Bravo region, and are all arid or semiarid. Most extinctions have occurred in Nuevo Leon ( 8) and Coahuila ( 7). The main causes of risk reported are: habitat reduction or alteration ( 86); water depletion ( 83); presence of exotics ( 76); small or declining population ( 73); and small habitat ( 57). All of which result in very local endemism. These causes of risk develop easily when the distribution is small. The critical factor is aridity, which is associated with desertization. Water conflicts were to be expected, and the result is resource non sustainability.