This study aims to compare between the marine alga Chaetomorpha vieillardi and the freshwater alga Cladophora glomerata. Water samples and massive growth of two species were collected from Port Said marine water pond and Ras El-Bar freshwater pond, respectively in 2019. The highly massive growth of Ch. vieillardi and C. glomerata, due to the trophic status and optimal physico-chemical properties of their habitats, causes ecological and economic problems. The very high massive growth of two species leads to relatively complete elimination of dissolved oxygen (DO) at the middle and bottom level of water during the second half of the night. Loss of DO values led to great loss of aquaculture. Although both algal species were belonging to the same family, yet they prefer different habitats where, Ch. vieillardi formed bloom in marine water but C. glomerata in freshwater. The significant variation in the biochemical, phytochemical compositions and heavy metal bioaccumulation capacity of Ch. vieillardi and C. glomerata could be attributed to the variation in biological properties of two species and the physicochemical characteristics of their habitats. Ch. vieillardi has higher carbohydrate and lipid content compared to C. glomerata. Most heavy metals accumulated in C. glomerata was more than that in Ch. vieillardi, but Cu and Fe were highly accumulated in Ch. vieillardi.