There were once over 60 offshore islands and patch reefs around Singapore, most of which were situated south of mainland Singapore. However, since the mid 1970s, major land reclamation was carried out on the mainland as well as the offshore southern islands. Most of the southern islands were reclaimed, adding 1695 ha to Singapore's total land area.

Some islands were merged as a result. The reef flats of many islands e.g. Pulau Sudong, Pulau Hantu and Kusu Island were reclaimed right up to the reef slope. Many of the coral reef organisms were smothered by the reclamation, while others were severely affected by the resulting increase in water turbidity. Since 1986, most coral reefs in Singapore have lost up to 65% of their live coral cover.

The high turbidity of our waters restrict light penetration and reef life ends at a depth of only 12m, marking the lower growth limit for hermatypic corals. Sedimentation rates ranged from 3-6mg/cm2/day in 1979. In 1994, these increased to 5-45mg/cm2/day (the higher value obtained from localised areas close to reclamation projects).

This reduced visibility from 10m in the 1960s to 2m or less today. As a consequence, the reef is very compact, as opposed to reefs in clear waters, which can be found at depths of 20m and more.