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The results of a survey of the sediment chemistry of 7 East Anglian reservoirs are presented as part of a regional study on the assessment and control of eutrophication . The influence of water quality (dissolved oxygen, pH, temperature) on phosphate (P0 4) adsorption by sediment from hypertrophic Ardleigh Reservoir is also examined . Extractable phosphate-P (extr .-P) varied between 92 and 383 mg kg -' dry matter. Extractable P varied between 5 .3 and 16 .6% of the total phosphate-P (Tot . P) content and increased with the concentration of dissolved reactive phosphate-P (DRP) in the overlying water column . Organically complexed iron (organic Fe) was the determinand which correlated most closely with phosphate adsorption capacity, PAC (r = 0.8). Organic Fe was also related inversely to Extr . P . The rate and extent of P0 4 adsorption by Ardleigh Reservoir sediment increased with the initial concentration of DRP and adsorption equilibria were reached after 24 h . The equilibrium DRP concentration, [DRP], was 0.7 mg P 1 -' under aerobic conditions indicative of a high potential for P04 exchange . The rate and extent of P0 4 adsorption was greater at 7 ° C than at 22 'C' P0 4 adsorption increased markedly with dissolved oxygen status. Ardleigh sediment exhibited a marked buffering capacity to a change in pH ; however, P0 4 adsorption was greatest at an equilibrium pH of 5 .6 and decreased progressively either side of this pH value.Options for the artificial control of sediment P0 4 release are discussed in relation to the seasonal variation in sediment P04 exchange observed for Ardleigh Reservoir .