The San Pedro Mezquital River (Spanish: Río San Pedro Mezquital) is a river of Nayarit, Mexico.

[1] The river originates in the Sierra Madre Occidental, and flows through Durango and Nayarit states to empty into the Pacific Ocean in Marismas Nacionales Biosphere Reserve.

[2] A few fish species are native to the San Pedro Mezquital River.

Among these are the two surviving Characodon splitfin species, which are both highly threatened.

[3] The extinct Durango shiner (Notropis aulidion) was native to the Rio Tunal, which forms the headwaters of the San Pedro Mezquital, a Pacific slope river rising near Durango City, Durango, Mexico (Chernoff and Miller 1986).