Around well-defined point sources, such as sewage outfalls, increased sediments and nutrients are known to cause local reduction in coral recruitment, increase mortality, and a shift in the balance of hard corals to non-reef building organisms. Around Phuket, there have been reports of a serious decline in marine water and reef quality. Coastal development, directly and indirectly related to tourism and its associated marine sewage outfalls, has been identified as the probable cause of this environmental degradation. As part of a broader study of the effects of water quality on reef ecosystems in the Phuket area, this study sought to gather evidence of a relationship between the intensity of tourism development,water quality and reef biota.