The atmospheric flux of cosmogenic7Be (53.3‐day half‐life) and the mode of7Be deposition in river‐estuarine and coastal environments have been examined. The atmospheric flux of7Be commonly supports inventories ranging from 1.0 to 2.0 pCi/cm2(1 pCi = 0.037 Bq). Beryllium 7 concentrations in water phase samples, collected across salinity gradients in several estuaries along the eastern coastline of the United States, range from 0.03 to 0.53 pCi/L and primarily reflect variations in7Be supply and sorption kinetics. The major process controlling the concentration of7Be on estuarine suspended particles appears to be the length of time that these particles remain in the water column. Field particle‐to‐water distribution coefficients for7Be have a median value of about 4 × 104but range over an order of magnitude reflecting short‐term variations in7Be input, particle dynamics, and particulate iron content rather than equilibrium sorption‐desorption responses to changes in water salinity or particle type. Residence times of7Be in the water column range from a few days in estuarine areas of rapid fine‐particle deposition, to several weeks in high‐energy environments where pronounced sediment resuspension reintroduces deposited7Be back into the water column. Inventories of7Be in sediments range from nondetectable to 3.3 pCi/cm2, with the highest inventories in areas where fine particles are accumulating rapidly. Such sites are also major repositories for other particle‐reactive substances. A7Be budget for the James estuary indicates that less than 5% of the expected7Be input is in the water column and that the short‐term estuarine trapping efficiency for atmospherically derived7Be is somewhe