The most significant cause of reef degradation in Singapore is sedimentation. Land reclamation, dredging of shipping channels and dumping of earth spoils, have increased the sediment load. Loss of coral reefs to land reclamation occurred along the southwest coast of the mainland and on some of the offshore southern islands. Increased sedimentation affected the remaining reefs in two ways 1) by causing a slow but steady reduction in live coral cover 2) by reducing the lower depth limit of coral growth on reef slopes. Surveys since 1986 indicated that live coral cover decreased by up to 20% on some reefs, although other reefs registered no impact. The reduction in sunlight penetration reduced the lower depth limit of coral growth. In the 1970s, coral growth extended to 10m down the reef slope. Today, growth is restricted to 6m although some coral species still occur at the 8m depth.
Accidental oil spills remain as an ever-present threat. However the 1997 Evoikos oil spill (27,000 tonnes) did not seriously affect coral reefs, although oil contaminated the upper parts of some reef flats.Other activities that also have an impact on the reefs include recreational and tourist-related use. Negligent or inexperienced divers without proper buoyancy control, leave a trail of broken corals. Anchor damage is caused by fishing boats and pleasure craft. At Pulau Hantu, a popular dive spot, courtesy mooring buoys were previously installed to prevent anchor damage.