The Buada Lagoon is the biggest and only true lake in Nauru, a small nation in Oceania consisting of a flat island of 21.3 km2 (8.2 sq mi) in area.

The Buada Lagoon, which is found in the southwest of the plateau that spreads over most of the central part of the island of Nauru, lies in the middle of a swampy depression of 12 hectares.

[8] This karstic bowl,[7] dominated in the northwest by Command Ridge, the island's highest point, came about as a result of sagging of the ground, itself arising from dissolving coral limestone, the mineral that makes up a great part of the plateau's rocks in the form of pinnacles, among which phosphate ore, of a high level of purity, is found.

[8][4] However, the lake's levels can vary considerable as a result of the Buada Lagoon's endoreic state; it has no outlet and is fed only by rainwater, there being no rivers at all in Nauru.

[11]: 74 The vegetation along the lake's edge to a great extent represents a relic of the tropical forest that occupied 90 per cent of the island before the phosphate ore began to be exploited in the 20th century.

[11] Covering 40 hectares (99 acres) and growing on a fertile, waterlogged soil,[7] it is made up mostly of tamanu (Calophyllum inophyllum) along with a few Rubiaceae like Guettarda speciosa.

[11] Within this forest, on small parcels of land, are grown fruit trees such as pandan, breadfruit, banana, mango, guava and soursop, as well as vegetables such as cabbage and bitter melon for consumption.

[4][13] Also grown are ylang-ylang, Cassia grandis, Crotalaria spectabilis, Samanea saman, seagrape and, for ornamentation, some Asteraceae such as Ageratum conyzoides and Synedrella nodiflora.

[8] Only one bird species, the Nauru reed warbler, is endemic, but it is threatened with extinction by habitat destruction, even though it has been colonising areas recently reforested now that phosphate deposits are no longer being exploited on the island's plateau.

So the Food and Agriculture Organization of the United Nations (FAO), at Nauru's request, from 1979 and 1980 put in place a programme to reduce the tilapia population.

Girded by a road, the lakeshore is made up of private residential properties[4] where fruit trees are grown, such as pandan, breadfruit, banana, mango, guava and soursop, and along with those such vegetables as cabbage and bitter melon.

[20]: 18  Despite these threats of environmental degradation, no protective measures are being undertaken, even though Buada Lagoon would seem to meet the criteria of the Ramsar Convention on Wetlands of International Importance.