the extraction of sand in the valley of the paraíba do sul river, carried out in a vulnerable environment, is responsible for significant environmental impacts. this work had the objective of investigating the increase of the total area of lakes created in the mining process for a period of 11 years and of verifying the influence of the evaporation from these lakes on the regional water balance. thus, a geographic information system data basis was implemented using the gis software package, spring, and landsat imagery. scenes 218/76 and 219/76 were used for the quantification of the mining areas and for the assessment of the evolution of the activity in the area for a period of 11 years. with data from a local climatological station (unitau/inmet-83784) integrated into the database and with the total area of artificial lakes resultant from sand mining activity, it was possible to estimate the increase of the evaporation rate due to this activity. an increase of 591 ha, in 1993 to 1,726 ha in 2003 in the area of lakes was observed. the resulting increase in the evaporating rate was 203% with 19,157,022 m3 evaporated in 2003 correspondent to the consumption of a city with more than 326,000 inhabitants, considering the average consumption for the state of s？o paulo which is greater than the brazilian average.