Since World War II, a major investigation has been pursued at Plymouth to establish the cause of the great changes which have taken place in the waters of the English Channel in the last 30 years. About 1930 a productive water, relatively rich in nutrients and macroplankton, was replaced by a poorer one. We sought the cause in the neighbouring shelf waters and found none. Whatever the cause, it was transmitted through the Atlantic Ocean. Today a level of nutrients similar to that found in the Channel in the 1920's occurs only at 700 m, from which no known mechanism can cause it to upwell.