The results of turbidity surveys carried out by the Fisheries Laboratory, Lowestoft in the southern North Seain 1957 and 1967 are described. The roles of such factors as water masses, phytoplankton production, bathymetry, wave action, tidal streams and bottom sediment in determining the turbidity distribution pattern are examined. It is demonstrated that the distribution of salinity, and hence the water masses, is in general similar to the distribution of turbidity, but that it differs in detail. The stronger tidal streams and finer bottom sediments in the western part of the Southern Bight are held to be the cause of these differences. The overall level of turbidity at any one time is shown to be influenced by the amount of wave action.