There is a growing concern that increased nutrient and sediment runoff from river catchments are a potential source of coral reef degradation. Degradation of reefs may affect the number of tourists visiting the reef and, consequently, the economic sectors that rely on healthy reefs for their income generation. This study uses a contingent behaviour approach to estimate the effect of reef degradation on demand for recreational dive and snorkel trips, for a case study of the Great Barrier Reef in Australia. Results from a negative binomial random effects panel model show that the consumer surplus current reef visitors derive from a diving or snorkelling trip is approximately A$185 per trip. Furthermore, results indicate that reef trips by divers and snorkellers could go down by as much as 80 per cent given a hypothetical decrease in coral and fish biodiversity. This corresponds to a decrease in tourism expenditure by divers and snorkellers on full-day reef trips in the Cairns management area of the Great Barrier Reef Marine Park of about A$103 million per year.