Flat Island (known as Ile Plate in French) is the largest islet found in the northern waters of Mauritius (11km off the northern Mauritian coast). It is 253 hectares in size and geologically consists of a thin coralline soil over the basaltic lava flows. Being the largest of the northern islets, Flat Island has the greatest conservation potential in the long run and as such has been declared a Nature Reserve under the Forests and Reserves Act 1983. Conservation works have been undertaken by the National Park and Conservation Service (NPCS) and Mauritius Wildlife Foundation (surveys and elimination of rats, mice and feral cats, 1998, monitoring). No threatened or restricted-range bird species are present, but the site is included because of its high potential for rehabilitation and exotic mammal eradication (mice, rats and feral cats).
The island is a recreation point for the local people mainly for swimming, fishing, snorkelling and poaching seabirds. Tourists usually visit the reefs offshore with few venturing far on land. The islet is relatively flat, hence the name, with a coastal area of about 20m wide on the northern, western and eastern sides; the coastal areas have a very thin leaf litter overlying the compacted sand. The south western part of the islet however has a high ridge of 102m with an automated lighthouse at the top. Flat Island has one of the only two lighthouse stations in Mauritius, although it is now abandoned, as are the other buildings and tracks found there. They date back to when the island was used as an isolation area for cholera sufferers and an animal quarantine station.
The islet has a forest coverage of approximately 30 hectares of mixed non native trees reaching a canopy height of over 8m. All other coastal areas of Flat Island are characterised by a high percentage cover of black spear grass (Heteropogon contortus) and occasional guinea grass (Panicum maximum) which are tall, highly invasive grasses in addition to West Indian Latana (Lantana camara) bushes. This habitat type covers a large area in the north and the area of higher topography in the south west. The vegetation has been greatly modified but still contains a number of indigenous species including Latania palm (Latania loddigessi), Vacoas (Pandamus vandermeerschii), Veloutier (Scaevola taccada), Bois Matelot (Suriana maritima) and Sainte Marie (Thespesia populnea), a coastal hibiscus.
Animals are not distributed on the whole island but rather cover about 1/3 of the island in different areas concentrated mostly in the south western part near the ridge. Birds living on the islet include the Wedged tail shearwater (Puffinus pacificus) and the Red tailed (Phaeton rubricauda) and White tailed tropic (P.lupturus).
North of Flat Island is Pigeon Rock, a spectacular bare rock stack used by resting and perhaps occasionally nesting seabirds. Exploring the islet is next to impossible without climbing gear which results in limited data about its flora and fauna.