Thecommunitystructureandbiodiversityofphytoplanktonwereinvestigated,andwaterqualitywasassessed,infourreservoirswithdifferenttrophicstates,inHubeiprovince,between2006and2008.Therewere215speciesofphytoplanktoninthefourreservoirs,rankedinorderofabundance:diatoms,Chlorella,andblue-greenalgae.Blue-greenalgaeoccurredprimarilyinthelayerabove,diatomsweremostabundantinthelayerbetweenSDand2SD,whereasotheralgae,including,weremainlyfoundinthelayerabove2SD.thanTheaveragedensityandcellsLand2.740mgand3.088mginTaoyuanheReservoir.Thedistributionofphytoplanktonbiomassamonglayerswasgenerallycharacterizedas:SD>surface>2SD>3SD>bottomexceptfortheDaoguanheReservoir,inwhichtheorderwassurface>SD>2SD>3SD>bottom.Therewasahighlysignificantdifference()andthePielouevennessindex(eservoirandtheother0.05)amongDaoguanhe,Taoyuanheandhereservoirs.Anegativecorrelationwasfoundbetweentotalnitrogenandphytoplanktonbiomass,ositivecorrelationexistedbetweentotalphosphorusandphytoplanktonbiomass.Variationsofphytoplanktoncommunitystructurewereprimarilyattributedtothedifferencesinthetrophiclevelsofthefourreservoirs.