This paper presents results of two monitoring programs carried out in two decades during April 1993-May 1994,and April 2015 May 2016 in the East Wadi of  El-Kébiri,  a protected area (PNEK) of eastern Numidia (northeastern Algeria). Monitoring was located in areas with different degrees of anthropogenic impacts.Selected environmental variables were recorded during the monitoring periods. . The Odonata fauna and biological indices were used to characterize development of the study area, after two decades and to assess the quality of the environment. The alteration of this river has resulted in a marked simplification of the original (1993-1994) odonatological fauna. Over the past two decades, odonatological species richness has decreased from 14 to 7 species inventoried during the 1993 and 2015 seasons. The phenology of adult was extended until early December 2015, possibly as a result of global warming. Odonata are identified as useful as indicators of environmental change in the monitored river systems. The majority of species such as the Gomphidae are not tolerant of increased contamination and changes in structure of the river. Only some species such as Lestes vridis, Platycnemis subdilatata, Ischnura graellsii and Ceriagrion tenellum, appear to be adapted to changed conditions and became dominant in heavily disturbed sites. The species disappeared from these sites are clearly associated with good water quality and less disturbance, which highlights the importance of the conservation of the habitats of freshwater and regular monitoring