This study aimed the multitemporal analysis of land use and coverage of the water supply, Alagados and its surroundings (1 km range) in Ponta Grossa city over ten years (from 2001 to 2011). Especially attention was laid on the marginal areas (100 m range) of the permanentpreservation areas (PPA). As the major water suply source of Ponta Grossa city, deterioration of water quality of Alagados is threatened bythe misuse and disorderly occupation of its surroundings .We used satellite images of medium spatial resolution (30 meters) and the objectoriented image method preceded by the image segmentation as the classification techniques. The results showed that there was a significantreduction in the surface of the water surface in 13.43% (88.15 ha) in the period 2001 to 2011, which shows a high sedimentation processoccurred in certain areas of the reservoir. Changes were also detected in the PPA range domain (100 meters) surrounding the reservoir,confirming a degradation process due mainly to the increase buildings occupations and agricultural practices.
