The State of Bahrain consists of more than 33 islands which vary considerably in size and structure. The largest island, known as Bahrain or Awal, is 48 km long from north to south and 16 km at its broadest. The islands lie in the South western waters of the Arabian Gulf. The total area of all islands is around 700 sq.km. The seas around the islands are shallow and rarely exceed 20 metres in depth. Salinities range from 40 parts per thousand in the north to 60 parts per thousand in the southwest.
The principal wetlands in Bahrain are coastal mudflats. These occur around many of the islands, and cover a large area in relation to the size of the country. The tidal regime is semi-diurnal, with a maximum annual tidal range of about 2.5 metres. The lowest spring tides occur during the night in the hot summer and during the day in winter. This regime has a beneficial effect on the inter-tidal flora and fauna, which would otherwise experience greater thermal stress.
Thousands of water birds utilize the abundant food resources available in the bay. Over 45 species of birds, mainly herons, shorebirds, gulls and terns, regularly visit the area during the migration periods and in winter.Many of Bahrain's smaller offshore islands support breeding colonies of seabirds and other wildlife.
Bahrain has been known for a long time for its many natural freshwater. Plantations of trees and agriculture have flourished because of the occurrence of these springs, and provide habitat which attracts many animals and migratory birds in particular.The largest inland wetland in Bahrain is the artificial lake known as Dumistan or Lawzi Lake. The salinity varies from almost fresh in the northern part of the lake to hypersaline at the southern end. Some waterbirds, such as Moorhen Gallinula chloropus and Black-winged Stilt Himantopus himantopus, have colonized the area and now breed there (Mohamed, 1993). Various studies have been carried out on the water chemistry of the lake and its microbiology.
A recent inventory of Important Bird Areas in the Middle East, sponsored by BirdLife International, identified four sites of special importance for bird conservation in Bahrain (Evans, 1994). Three of these are coastal wetlands of considerable importance for waterfowl and seabirds, namely Tubli Bay, the southwest coast of Bahrain Island, and the Hawar Islands. All three are included in the present inventory, along with one other coastal wetland (Ras Hayan) and the artificial Lawzi Lake.