Problems of pollution from nutrients in the effluents of prawn farms have often been highlighted, leading to questions about their sustainability. This study aimed at the monitoring of nutrient and chlorophyII a levels in two penaeid prawn grow-out ponds in West Malaysia, one under intensive culture (located in Penang), and the other under semi-intensive culture (pond located in Ban Merbok, Kedah). The nutrient levels and their possible effects on the surrounding coastal waters were analyzed. During the first month of the grow-out phase, the phosphate (PO₄-P) concentration appeared to be very high, but during this period there was no water change in the pond. The nitrite (NO₂-N) levels in the pond in Penang during the grow-out phase and in both ponds during harvest satisfied the criteria for the penaeid prawn pond effluent standards proposed by the Pollution Control Department, Thailand. The nitrate (NO₃-N) levels in the ponds were of the same order as the NO₃-N levels recorded in mangrove estuaries. The parameter of concern in terms of pollution appeared to be mainly the concentration of ammonia (NH₄-N) during the harvest phase. The NH₄-N value during harvest exceeded (Ban Merbok) or was near (Penang) the criteria for concentrations of total ammonia recommended by USEPA (1993). It is suggested that effluents during harvest be channeled into oxidation ponds where the levels of ammonia and suspended matter could be reduced by the nitrification process and sedimentation.