We examined monthly variation in the characteristics of river sections along the Río Salado (Puebla, Mexico) and how these factors were associated with the dis- tribution of the tadpoles of the toad Ollotis occidentalis. Tadpoles were observed in the river in March 2007, and from November 2007 through February 2008 and were only found in the main river channel. Sections of the Río Salado with tadpoles were deeper, wider, and longer than sections without tadpoles. Dissolved oxygen levels were higher and salinity was lower in river sections with tadpoles compared to the sections without tadpoles. There was no difference in temperature between sections with and without tadpoles. Tadpoles were found in river sections that contained more vegeta- tion than river section without tadpoles. Our results suggest that the distribution of tadpoles of O. occidentalis is related to the permanence of water, the chemical nature of the water, and the presence of vegetation
