The aim of this work was to be informed and aware of the red tide conditions before the entering of algal blooms in seawater supply canals of the shrimp farm and hatchery complexes in Bushehr Province. Field investigations and monthly samplings have been carried out to determine environmental parameters, nutrients, chlorophyll–a and phytoplankton in the southern part of the input water channels of Mond, Delvar and Heleh farmed shrimp complexes from April to December 2011. The identified phytoplankton belonged to three classes of Bacillariophyceae, Dinophyceae and Cyanophyceae.  12 genera belonging to Dinophyceae, 25 genera to Bacillariophyceae and two genera to Cyanophyceae were observed during the study. The highest average density of total phytoplankton was recorded at Heleh station at 18374 cells/lit. The maximum density of phytoplankton was at Delvar station in December. The highest density of Dinophyceae was observed in August. Alexandrium sp., Ornithocercus and Prorocentrum sp. were the predominant species of Dinophyceae class. Bacillariophyceaes are thermo-tolerant and halo-tolerant while Dinophyceaes and Cyanophyceaes are thermo-intolerant and halo-intolerant. Bacillariophyceaes are silica limited while Dinophyceaes are phosphorus limited phytoplankton