The dataset contains records of Butterflies (Lepidoptera) collected in the lower valley of the River Tua, and included in the Ecological Monitoring Program (2011-2017) of the Foz Tua Hydroelectric Dam, promoted by EDP – Energias de Portugal, S.A. Data were collected between July 2014 and August 2017 during field visits to 33 sampling transects with favorable habitats on the area of the lower Tua valley directly or indirectly affected by the Foz Tua dam, and in a small stream of the Douro basin. The occurrence of the target species was recorded when individuals were seen or captured in the selected transects.