The aim of this study was to know the chemical effect of the freezing process on the quality of fish and to know the water pollution by some heavy metals and the reflection of this pollution on fish. A total of 50 random samples fresh and frozen fish were collected from Manzala lake in Dakahlia Governorate (25fresh fish). Also, from the different markets in Mansoura (25 frozen fish) and 25 samples of water were collected randomly from Manzala Lake in Dakahlia Governorate. All samples were examined chemically. The results showed an increase in Cadmium in tissues of fresh and frozen fish and increase in copper in tissues of frozen fish. Meanwhile the water samples showed increase in lead, cadmium and copper. Concerning total basic nitrogen, thiobarbituric acid and histamine levels they were above the permissible limits in frozen fish, while in fresh fish were within permissible limits. From the above we can conclude that the exposure of fish in water to some heavy metals lead to perception of these heavy metals in tissues of fish as well as freezing of fish lead to negative chemical changes, represented by increase of total volatile basic nitrogen, thiobarbituric acid and histamine,therefore fresh fish should be consumed as soon as possible and surely within 3 days from purchased because of longer storage may result in rapid rise in total volatile basic nitrogen, thiobarbituric acid and histamine, that causes a potential threat to consumers health.