This paper aims to apply the digital processing of satellite images to assess the relationship between the expansion of impermeable surfaces and cyanobacterial proliferation. For this purpose, the Billings reservoir, located in the Metropolitan Region of São Paulo, Brazil, was adopted as the object of the study. The urban expansion in the hydrological watershed where this reservoir is located and the increase of cyanobacteria concentration in its water were quantified. The results show that there is a positive linear relationship between the increase in impervious surfaces and the proliferation of cyanobacterial colonies. However, this study did not quantify this relationship, which is intended to be explored in future works..