[Bacteriological quality of Bendetti Lake (Santo Tomé, Santa Fe Province, Argentina) and associated environmental variables].

The main objective was to determine the bacteriological quality of a shallow lake in the lower Salado River Basin (Bedetti, 31 degrees 40' S and 60 degrees 45' W). Seventy samples were tested by the most probable number (MPN) method, throughout three years. The number of thermotolerant coliforms was very variable: from 20 MPN/100 ml to 130,000 MPN/100 ml. These variations were mainly associated to the local rains (rs = 0.4853, p = 0.0001) and to the hydrometric level-h-(rs = 0.3835, p = 0.008). Statistically significant correlations between coliform bacteria and other variables (temperature, oxygen, pH, conductivity and transparency) were not found. The increase of coliforms associated to the increase of the hydrometric level indicates the presence of diffuse contamination sources. It was found that the rains affected the bacteriological quality, specially during the low water periods (h < 3.60). During the high water periods (h > 4.70) one of the main coliform contributor was represented by the incoming floating islans and aquatic macrophyte, from allochthonous fluvial systems. The coliform concentrations between the Bedetti lake and the Salado river were compared. The results show a better bacteriological quality of the lake (geometric average = 1,990/100 ml vs. 420/100 ml, n = 56) so that, connecting them by the construction of an artificial channel is not advisable.