The potencial standing crop of oyster Crassostrea rhizophorae has been calculated as 938,6 tons oyster meat per year (wet-weight) for market sized oyster, in the northern zone of the Cienaga Grande de Santa Marta. It has been estimated that the oyster-bank area within this zones covers 3.000.000 sq.m. The calculated actual oyster standing crop for that area during this research (April-November 1982) was 3,9 tons of oyster-meat (wet-weight) and the actual catch 2,0 tons (in the same period). This reduction in the actual standing crop of oyster is mainly the result of: 1. The low prolonged salinity and the sediment causes mass mortality on oyster population; 2. Deterioration of the quality and available amounts of supporting shell substratum, required by oyster seedling attach and growth until they reach comercial size.