Hong Kong imposed a partial restriction on application of organotin-based antifouling paints in 1992. Since September 2008, the International Maritime Organization prohibited the use of such antifouling systems on all sea-going vessels globally. Therefore, it is anticipated a gradual reduction of organotin contamination in Hong Kong's marine waters. Using the rock shell Reishia clavigera as a biomonitor, we evaluated the organotin contamination along Hong Kong's coastal waters over the past two decades (1990-2015). In 2010 and 2015, adult R. clavigera were examined for imposex status and analysed for tissue concentrations of six organotins. We consistently found 100% imposex incidence in female R. clavigera across all sites. Tissue triphenyltin (TPT) concentrations were high in most samples. A probabilistic risk assessment showed that there were over 69% of chance that local R. clavigera would be at risk due to exposure to phenyltins. Comparing with those of previous surveys (2004-2010), both imposex levels and tissue concentrations of organotins did not decline, while the ecological risks due to exposure to organotins were increasing. We also observed high concentrations of monobutyltin and TPT in seawater and sediment from locations with intense shipping activities and from stormwater or sewage discharge. Overall, organotins are still prevalent in Hong Kong's marine waters showing that the global convention alone may be inadequate in reducing organotin contamination in a busy international port like Hong Kong. Appropriate management actions should be taken to control the use and release of organotins in Hong Kong and South China.