El Mex Bay area received domestic, industrial and agricultural waste water from the surrounding area. The need to pay much attention to the potential effects of anthropogenic inputs upon the hydrochemical characteristics of the bay is an emergency. Several water samples have been analyzed for physico-chemical characteristics during 2010/2011: Seven samples from El Mex bay and 4 samples from drains. The study revealed that pH, salinity, dissolved oxygen, oxidizable organic matter, biological oxygen demand, and chlorophylls-a,b.c, were in the ranges 7.16-8.97; 0.3–42.04; ND–22.26 mg/L; 0.4–112.00 mg O2 /L; 3.23–111.29 mg/L; 0.11–241.91 µg/L; 0.03-242.78 µg/L and 0.01-239.55 µg/L, respectively. The increasing organic supply introduced into the studied restricted area characterized by its relative slow rate of self-purification results in elevation of OOM compared to previous studies. The ranges of nutrients (μM/L) were: 0.15-2815.85, 0.28–22.85, 0.2–58.42, 0.25-30.45 and 0.11-40.23 for ammonia, nitrite, nitrate, reactive phosphate and reactive silicate, respectively. Principle Component Analysis (PCA) which was used to develop water quality index (WQI) revealed that El-Dekhila Head and El Qalaa drain were the most polluted sampling sites that resulted from the disposal of industrial, agricultural and domestic wastes. Depending on DIN/DIP ratio of seawater for El-Mex Bay and adjacent drains the majority of the investigated area sums to be P-limited.
Key words: Seawater quality,El-Mex bay, drains, Alexandria, Egypt, nutrient salts, hydrographic characteristics.