The western coastal water of Alexandria is affected by different drainage sources from land. This area receives fresh and brackish water from El-Mex pumping station and El-Noubareya Canal respectively. Also, domestic sewage
and industrial wastes are discharged into the sea area of El-Mex and Western Harbour of Alexandria.
The main objective of this paper is to study the spatial and temporal changes of El-Mex and Western Harbour waters and monitor the plumes of different pollutants with accepted level of accuracy for practical control. This
task could be executed by applying Principal Component Analysis (PCA) technique to some physical observations of sea water (temperature, salinity, density and dissolved oxygen). The resulted PCAs from different layers of temperature, salinity, density and dissolved oxygen distributions (horizontal and vertical) showed three
dominant water masses. The first water mass was found close to the shore and covered most of the water column inside the Western Harbour. Also, it extended far from the shore line to cover most of the surface layer. The second one was
found at El-Dekhilla area and distributed to the northern and eastern directions.
The third one was found at El-Mex Bay water, nearly covered the subsurface water and extended to offshore water. Other water masses depend on the spatial variations. The PCAs showed that the water masses and circulation pattern inside the
Western Harbour and at El-Mex Bay could be highly identified. Also, different plumes of pollutants that are discharged from land into sea could be monitored
clearly.