The nature and the quantity of run-off into coastal waters will to a large extent influence the occurrence and distribution of a number of chemical components such as nutrient salts, organic matter and trace metals in these waters. In open coastal environments the run-off is usually quickly dispersed and diluted so that little of it remains at concentrated levels in the vicinity of the discharge point. On the other hand, if such discharge is made into closed or confined waters, the rate of dispersal will depend on the circulation pattern and the rate of flushing of the run-off. Thus in some areas where the circulation is restricted, a build up of compounds may occur which, depending on the run-off composition, may have a marked effect on the ecology of these waters. The situation may be further aggravated if the run-off includes large quantities of industrial and domestic waste.