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The phytoplankton of a tidal creek in Lagos was investigated for six months (September 1998-February 1999). The physico-chemical environment was essentially neutral (pH 7.00-7.30), relatively more transparent (> 0.23 m), expressed higher conductivity (> 0.10 mS cm(-1)), higher chloride values (> 23.48 mg L(-1)), lower nitrate content (< 0.70 mg L(-1)), lower sulphate values (< 0.45 mg L(-1)) and phosphate values (< 0.12 mg L(-1)) in the dry months. In the wet months, September to November 1998, conductivity (< 0.16 mS cm(-1)), transparency (< 0.80 m), salinity (< 0.04%), dissolved oxygen (< 24.00 mg L(-1)), chloride (< 24.21 mg L(-1)) and phosphate (< 0.21 mg L(-1)) were recorded. The phytoplankton was dominated by diatoms (48 pennate forms and 23 centric forms). The other algal groups comprised six blue- green algae and six green algae. Species richness (d) was high in stations nearer the Lagos lagoon for the six sampling periods. Shannon-Weaver index (H1) was lowest in November 1998 and highest in October 1998 and February 1999 while evenness of species J was low (< 0.71) throughout the period. Higher phytoplankton biomass was recorded in the dry months than wet months.

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Physico-chemical parameters have been observed to influence phytoplankton composition of coastal areas and water in Nigeria. In order to assess this, the phytoplankton composition of a tidal creek in Lagos was investigated in relation to the physico-chemical characteristics for twelve months (February 2010-January 2011. Six stations were created, phytoplankton samples were collected using 55µm mesh size plankton net and water samples were also collected for physico-chemical parameters analysis. Four major divisions, Bacillariophyta (78%), Chlorophyta (11%), Cyanophyta (10%) and Euglenophyta (0.07%) were documented. The phytoplankton abundance was influenced by parameters such as rainfall, phosphate-phosphorus, nitrate-nitrogen and salinity. and October 2010 (station C) respectively. Human induced stressors such as dredging, sand mining and poor sewage system might have affected the phytoplankton composition of the studied area.