In this study, containing a database covering such the period from January 2008 to December 2010, on the water level of the Hammam Bougrara dam located in a semi-arid zone with moderate winter (western Algeria), we focused specifically on the mechanisms of eutrophication as well as the spatial and temporal variation of the physico-chemical and biological characteristics of the reservoir. The diagnosis revealed high concentrations of certain elements such as P, PO4, NO3, NO2, NH4, Na+, Ca2+, Mg2+, K+, Cl-,HCO_3^- and SO_4^(-2),, which characterizes highly mineralized waters with conductivities between 1100 and 1800 S / cm, therefore polluted and selenitic. These waters are rich in nutrients, such as phosphorus and with a slightly alkaline pH (between 7.1 and 9.1) favor the proliferation of organisms such as Chlorophyceae, Cyanophyceae and Diatomophycéeswhich together account 93 57% of the population of algae. This proliferation causes a decrease in transparency and dissolved oxygen which are also signs of eutrophication. This study will adopt a better methodological approach to reduce the number of stations and increase the sampling rate, for a thorough understanding of limnology operation of the dam to ensure its protection. Despite the very high phosphorus inlakes during those years, the symptoms of eutrophication in the reservoir (chlorophyll a.) Are far from achieving the expected levels of extreme loads on the flow-replies Vollenweider. This could be explained by the fact that, upon his arrival for restraint, ortho-phosphate is quickly rendered inaccessible due to algae efficient flocculation means of fine clay particles and a formation hydroxyapatite followed by precipitation. Consequently, one can conclude that it would be necessary to develop and deepen our knowledge of limnology of lakes and reservoirs in temperate climates, especially in arid and semi-arid areas, in order to embed processes in these lakes a general model describing the relationship load-response, similar to that of Vollenweider. The results could help to set specific objectives for reducing phosphorus inputs depending on the intended use of the waters and allow better management of water quality in terms of trophic answer and that in the context of sustainable development and decision support.