Agricultural run-off from the Great Barrier Reef catchment area may cause degradation of coral reefs, affecting the tourism sector that relies on healthy reefs for its income generation. A Contingent Behaviour approach is used to determine the effect of reef degradation on demand for recreational dive and snorkel trips, for a case study of the Great Barrier Reef (GBR) in Australia. We assessed how reef degradation affects GBR tourism and to what extent reef-trip demand depends on the visitors' socio-economic characteristics. A count data model is developed, and results indicate that an average visitor would undertake about 60% less trips to the GBR per year, given a combined 80%, 30% and 70% decrease in coral cover, coral diversity and fish diversity, respectively. This corresponds to a decrease in tourism expenditure for reef trips in the Great Barrier Reef Marine Park area of about A$ 136 million per year.