Platte Island, 140km due south of Mahé, is low and flat with an encircling reef containing a lagoon. Known for its rich fish life, Platte has an airstrip and is occasionally serviced by Island Development Company (IDC) aircraft from Mahé.
The island, a low and wooded sand cay, is about 1250 meters long north-south, with a width from 250m in the south to 550m in the north, with a land area of 0.65km². The island is bisected by a 900-meter-airfield that follow the long north-south axis. There is a small settlement on the western shore with the manager's house and a few guest cottages to the northwest. Barrier reefs, over which the sea breaks heavily, extend 5km north, about 0.8km east, and 2.4km south of the island, making it a pseudo-atoll. Within the barrier reefs, the lagoon is quite smooth, and landing is safe and easy. A submerged reef rim extends 12km west and 18km south of the island, obviously the remnants of a sunken atoll, creating a complex of almost 25km in length north-south and 14km in width east-west and covering an area of roughly 270km².
There are two passages through the reef on the northwest side, available for small vessels with local knowledge only. La Perle Reef lies at the southwestern end of the reef rim, about 10km southwest of Platte Island. Depths of less than four meters can exist on this reef where breakers have been observed.