Samples of water and snails collected through aleatory scoops in a small dam were done to obtain data concerning the physical and chemical characteristics of the water and their possible influence on biological aspects of the life cycle of snails. Among the 17 analysed parameters, Alkalinity and Conductivity showed a positive correlation with the density of B. tenagophila (r = +0.224 and r = +0.290), while CO2 and Acidity were negatively correlated with this populacional parameter (r = -0.592 and 0.601). Alkalinity and Total Hardness values were slightly higher than 100 mg/l CaCO3. Chlorides and Conductivity showed means of 94.9 +/- 38.7 and 680.1 +/- 643 microS/cm; these values are very high for that region. Other factors like pH and OD are according to the pattern for provision untreated waters. The density of B. tenagophila declined in the 6th month after a long period of torrential rains and in the rainy summers. In the colder months of the following year the density was higher (until 124 individuals/months/90 scoops). The monthly mean of the diameters of the snails was always larger than 13 mm, reaching 21.4 +/- 4.1 mm, but the mode was about 17 mm. There was no correlation between diameter/density (r = 0.037) and density/temperature (r = 0.065).