The Brazos water snake or Harter's water snake (Nerodia harteri) is a species of mostly aquatic, nonvenomous, colubrid snake native to the United States. It is found only in north-central Texas along the Brazos River system. Due to its limited range, it is considered to be a threatened species in the State of Texas. The epithet harteri is in honor of Peter Harter, who collected the first specimen in Palo Pinto County in 1936.