The water quality of Lake Mariut has been deteriorated for about 5 decades due to continuous discharge of agricultural, municipal, and industrial wastes from Alexandria City and the adjacent land. During the past two decades, some steps were taken for rehabilitation of the lake through primary treatment of the discharged wastes and insulation of the polluted wastewater of QD from the water body in the main basin of the lake. Several parameters of water quality at the surface and near bottom were measured at twelve locations during winter (January) and summer (August) of 2013 and 2014. The present study revealed that the lake water appeared to be well aerated but still containing high concentrations of N and P and suffering hyper-eutrophic conditions. The water quality index (WQI) reflected medium condition in the lake and bad condition in the diverted drains. The P-budget calculation displayed that TP input into the LMMB from UD us and resuspension process from sediments exceeded the output by out flowing at UD ds and settling.

Due to the acute water scarcity facing many urban areas, the water resource management, and lake rehabilitation become a global interest. Before applying the appropriate approach in the rehabilitation (restoration) of a hypereutrophic lake, the assessing of the point sources of pollution and their effects are A MUST. Lake Mariut is an example of lentic polymictic closed coastal Egyptian lake. The economic and recreational values of Lake Mariut were deteriorated since 1960s, as a result of using its Main Basin as a sink of wastewaters discharged from the agricultural Umum Drain and the heavily polluted Qalaa Drain mixed with primary treated sewage waters from Alexandria East Wastewater Treatment Plant. The aim of the current study is to find the suitable solution/s for the Lake Mariut Main Basin restoration, by (1) studying the general characteristics of its drainage water system (Umum and Qalaa Drains) at their downstream parts before reaching the lake at its southern side as well as the adjacent non-polluted Lake Mariut Fishery Basin. (2) Discussing (by calculation) the applicability of two proposed improvement solutions. The results reveal that, in the first the water quality of the anoxic Qalaa Drain must be improved by diluting its waters with oxic Umum Drain waters via Lake Mariut Fishery Basin prior discharging. This solution is found not sounding as it difficult to attain from practical point of view. The other alternative is by diverting the polluted Qalaa Drain point source itself away from Lake Mariut Main Basin water body which is sounding and highly recommended.

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Water resource management and lake rehabilitation are global interest, to overcome the acute water scarcity facing most urban areas, especially in developing countries. Lake Mariut (LM) is an Egyptian lake that lies south of the Mediterranean Sea, and its management had a great interest in Alexandria’s future development and as a part of the environmental sustainability of the Mediterranean basin. LM consists of 4 major basins, namely, main (MB), northwest (NWB), southwest (SWB), and fishery (FB). The MB has deteriorated as it consistently received (sewage and industrial) wastewaters till 2010. This was the date of diversion of the polluting sources as a rehabilitation step. The present work is made after elapsing 8 years from the diversion and aims at monitoring and assessing the status of the water quality not only of MB but also for the other 3 basins too. This was carried out twice, one in cold winter and the other in warm summer. The parameters studied were physico-chemical including water temperature, pH, dissolved oxygen/hydrogen sulfide (DO/H2S), salinity, and chlorophyll a besides nutrient salts (nitrogen, N and phosphorus, P compounds). The results revealed that the waters of both MB and SWB basins were depleted in DO to a level difficult to sustain fish life and showed elevated levels of most nutrient salts. Trophically, all the studied basins were in eutrophic-hypereutrophic condition. As a result of pollution source diversion away from MB to be discharged in the downstream part of Umum Drain (UD), the levels of TN and TP entering Mex Bay through UD were slightly higher than the permissible limit and lower than dangerous loading. The applying of principle component analysis (PCA)-based classification approach, for obtaining the WQI on the current study, revealed that the FB, NWB, and SWB2000 showed a relatively good water quality when compared with MB. The depletion in the vital DO is catastrophic and needs urgent solution/s. One of the proposed solutions is the dredging of bottom spoiled organic-rich sediments. This and other suggested solutions are, however, discussed, evaluated, and presented.

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