Divers mine shallow-water diamonds on the west coasts of South Africa and Namibia. In the process they cut kelp, suck up gravel that is sorted on the shore and then deposited intertidally, and uncover and overturn subtidal boulders.The impacts of these divers on intertidal and subtidal reefs, and on the population structure of the commercially important rock lobster Jasus lalandii, were monitored for 5 years near Lüderitz in southern Namibia. Sampling was undertaken at unmined reference (control) sites and at sites mined at various times in the past. Percentage cover and densities of benthic organisms were recorded, and the abundance, length-frequencies and sex ratios of rock lobsters determined.