It is well known that river channels can act as significant sediment stores, attenuating the flux of fine sediment through the fluvial system. Such storage of fine sediment also has important implications for sediment-associated phosphorus (P) fluxes, through both P storage and water-sediment interactions, which may lead to P uptake and increased P concentrations in sediment. In order to explore these mechanisms further, spatial and temporal variations in both the P content of fine bed sediment and associated P storage have been studied in three lowland catchments of contrasting geologies in the UK, namely the River Tern in Shropshire and the Rivers Pang and Lambourn in Berkshire. Fine bed sediment was sampled in representative reaches on a bi-monthly basis using a re-suspension cylinder, and the resulting samples were analysed for total P, inorganic, organic and algal available P and particle size. On a spatial scale, the results demonstrate significant between and within catchment variations in sediment-associated P concentrations and storage, which in turn reflect catchment characteristics and the magnitude and location of anthropogenic inputs. Significant temporal variations in both storage and concentrations were also evident, with maximum and minimum total P concentrations and storage occurring in late summer and winter respectively. Temporal variations in total P concentration were mirrored by the P fractions, which also showed late summer maxima and winter minima. Temporal variations in P concentration reflect both the residence time of the sediment and the ambient dissolved P concentrations, while variations in storage are mainly due to hydrological regimes. Overall, the study highlights the need to consider both spatial and temporal controls on the mechanisms governing P storage associated with fine channel bed sediments.