The phycological and physico - chemical evaluation was performed in three fish farms at northeast of Damietta (Boghdady, Dorgham and Moamen) as well as their irrigation canals over the period from May 2001 to April 2002. The species number was negatively correlated with water salinity and pollution. The data revealed 32, 25 and 28 species number inside the three fish farms Boghdady, Dorgham and Moamin, respectively. Such number increased to become 96, 72 and 56 respectively at these canals. Phytoplankton biomass was relatively higher in fish farms than that in irrigation canals. Cyanophyta, Bacillariophyta and Pyrrophyta were mostly the dominant phytoplanktonic groups in the different stations. Phycological indices  indicated that water was moderately polluted (b-mesosaprobic) in the irrigation canals and heavily polluted (polysaprobic) in the fish farms. There was also low net oxygen production by phytoplankton and high biological oxygen demand in fish farms. The depletion of the dissolved oxygen especially during second half of night in addition to the high concentration of ammonia might lead to fish mortality in subsurface water of fish farms.