1. A number of planktonic cyanobacteria species form resting stages that survive in the sediments of lakes. The significance of this life history strategy to the ecology of new planktonic populations was investigated in Esthwaite Water, a mesotrophic lake in the English Lake District. 2. A simple trapping technique was used to quantify vertical movements of five species of buoyant gas-vacuolate cyanobacteria from close to the sediments, along a depth transect. 3. 'Recruitment' from the sediments was found to be widespread amongst the cyanobacteria species associated with the summer phytoplankton community. 4. Estimates of the vertical upward fluxes of cyanobacteria based upon trap catches could not account for observed increases in the planktonic populations suggesting that 'recruitment' was not a significant source of biomass. 5. Vertical upward movements of Anabaena solitaria were recorded prior to this species becoming established in the plankton suggesting that benthic populations might be a source of cells for initial pelagic growth of populations of this species. 6. Low numbers of vegetative filaments of Anabaena flos-aquae, Aphanizomenon flos-aquae and Oscillatoria agardhii were observed in the plankton through the winter. These small overwintering populations appeared to be the primary source of inocula for the large summer populations of these species.