Runoff and sewage discharge from land developments can cause significant changes in water quality of
coastal waters, resulting in coral degradation. Coastal waters around Phuket, Thailand are influenced by
numerous sewage outfalls associated with rapid tourism development. Water quality and biological
monitoring around the Phuket region was undertaken to quantify water quality and biotic characteristics
at various distances from sewage outfalls. The surveys revealed strong gradients in water quality and biotic
characteristics associated with tourism concentration levels as well as seasonal variability. Water and
reef quality tended to decrease with increasing tourist intensity, but improved with increasing distance
from sewage discharge within each of the three study locations. In addition, the effect of wastewater discharge
was not localised around the source of pollution, but appeared to be transported to non-developed
sites by currents, and exacerbated in the wet season.