Runoff and sewage discharges from tourist resorts can cause serious adverse impacts on coral reef communities. These impacts result from both the contaminants contained in the discharges and from the freshwater carrier itself. Of the many components of sewage, the nutrients nitrogen and phosphorus appear to cause the most severe adverse impacts. The main effects of nutrients on corals appear to be indirect. The higher nutrient levels result in increased algal growth which can ultimately lead to complete destruction of the delicately balanced coral reef ecosystem. The available evidence implies that denitrification and phosphorus removal are necessary treatment requirements if acceptable levels (after dilution) of these components are to be achieved. The disposal of run-off needs to be considered carefully. Factors such as re-diversion, storage, reuse, treatment for removal of nutrients and disposal via submarine outfall all need to be considered.