In the Andes of Peru, important glaciers masses still exist between 4500 and 6700 m asl. On some representative glaciers, a strong retreat at the terminus has been measured during the last decades. This explains the constant formation of new glacier lakes, some of them being dangerous. Moreover, continuation of this trend could limit water resources of the Cordillera, modifying runoff of streams, principally during the dry season. Some data about glacier retreat in Cordillera Blanca are presented. With a good knowledge of this evolution, it was possible to carry out works aiming at reducing or suppressing the risks coming from the lakes. In the same time, some lakes were converted into reservoirs to satisfy demand from agriculture, domestic consumption, energy and industry.