ABS>A proposal was made to discharge mildly radioactive liquid effluent, arising at the new Atomic Energy Establishment at Winfrith Heath, into the sea off the Dorset coast. Experiments are described which were performed at sea from August to November 1958 to determine the rate of sea dilution of a tracer dye by sampling and analysis under varying weather and tidal conditions, to determine significant gradients capable of influencing dilution rates, to obtain data on tidal streams, to sample marine life and deposits from the sea bed, and to study the contour of the sea bed in the area. Results are summarized. (C.H.)