In the Gulf/Trench of Cariaco and the Gulf of Paria, the transparency of the water body was determined by means of Secchi disk. The average Secchi-depth (Ds) that was calculated for the Gulf of Cariaco was 10.0 m, for the Cariaco Trench it was 11.9 m and for the Gulf of Paria was 3.2 m. Chlorophyll a exerted control over the water transparency of the Gulf/Trench of Cariaco, but in didn't show to have any influence in the Gulf of Paria. The "rest" (total attenuation minus chlorophyll and water) showed the greatest absolute variation among the considered factors in the last mentioned area. It can be concluded that Secchi disk reading in the Gulf of Paria cannot be related to the amount of chlorophyll a in the euphotic layer. Further the turbidity that was observed in the last mentioned area reduces the potential productivity that could be expected from the chlorophyll a reading, because the calculated compensation depth was located to near to the surface.