The forereef continues to slope eastward to the reef wall, which drops vertically into the depths. Coral Atolls - The final reef type, seaward of the continental shelf is composed of the three coral atolls. Turneffe Islands, the largest of the atolls, has a maximum length of 30 miles and varies in width up to a maximum of 10 miles. Numerous mangrove covered sand cays, in a variety of sizes, rim Turneffe. The interior of the atoll is carpeted with vast meadows of seagrass.
Diving is excellent off the southern tip of the atoll.
Lighthouse Reef is the smallest of the three atolls. This atoll is surrounded by a well developed reef-rim with only three major gaps. Halfmoon Cay Natural Monument lies along the southeastern portion of the reef and the Blue Hole Protected area lies within the interior of the atoll. Lighthouse Reef supports a remarkable diversity of living reef and reef-flat areas, well developed spur and groove zones, and a unique arc shaped reef segment which lies on the southwest corner of the reef. The greatest length of Glover's Reef is 15 miles and its greatest width is 6.5 miles.