Sea water contaminated with diluted radioactive effluent originating from Sellafield Reprocessing Plant inundates saltmarshes in the Esk estuary of west Cumbria (UK). Much of the radioactivity on the saltmarsh vegetation was found to be associated with a surface deposit of silt, brought onto the area during tidal inundation. Large temporal variations in the radionuclide concentrations of the vegetation were found, these being due probably to seasonal fluctuations in the extent of silt deposits. The grazing habits of sheep were studied on one of these saltmarshes and the consequent ingestion of radionuclides by the sheep was estimated. The sheep ingested different quantities of radionuclides according to the time of year as a result of a combination of radionuclides on the saltmarsh vegetation and the seasonal grazing behaviour of the sheep.