Morocco is one of the countries most affected by the scarcity of water resources and the poor distribution of rainfall. Natural lagoon is the most treatment processes used in Morocco. in-deed, Morocco is a sunny country throughout the year as well as the lagoon system it requires minimal effort in operation and maintenance. Moreover, this system is the best process for removing bacteria indicators. For these reasons, we carried out a study of the purification per-formance of natural lagoons during five years, located in Chichaoua region (Morocco). The lagoon system was monitored for five years, with measurements taken every three months at the input and output of the system. It received a hydraulic loading rate (HLR) between 1171 and 2760 m3 with an average of 2053 m3/day. Obtained results show the removal of 37% of TSS, 63% of BOD5, 60 % of COD, 61% of NH4+, 37% of TP, and 6.5 log units of coliforms during the mentioned monitoring period . Thus, the effluent values do not always comply with the Moroccan water quality requirement for irrigation reuse. Additionally, the statistical anal-yses confirm the presence of a strong linear correlation between almost all variables in the la-goon output. Therefore, the performance efficiency of the lagoon in removing organic matter and nutrients was significantly (p <0.05) dependent on the season period. However, the fecal contamination was not significantly (p > 0.05) affected by the seasons in this study. At the end of this study, we have proposed a complementary treatment before the reuse of treated wastewater.