Lake Eyre, a great salt lake of tectonic origin, lies asymmetrically in the south-western corner of the closed inland drainage basin in the heart of the Australian continent. With an area of 1,140,000 km2, Lake Eyre Basin is the largest Australian drainage division apart from the Western Plateau and is one of the largest areas of internal drainage in the world. The lake, whose lowest parts lie 15.2 m below sea level, consists of two sections. Lake Eyre North, 144 km long and 77 km wide, is joined by the narrow Goyder Channel to Lake Eyre South, which is 64 km long and 24 km in width. Not so long ago it was considered to be permanently dry, but the last forty years have witnessed some twenty flood events, with the most spectacular fillings occurring in 1950, 1974 and 1984.

The deepest region of Lake Eyre North is the eastern part of Belt Bay in which bottom levels were found the lowest point on the Australian continent. The floor of the lake is very flat, therefore the definition of the exact location is rather difficult. The shores of the lake are well defined and consist of sand dunes, cliffs of eroded gypseous loam or low rocky escarpments. The south-eastern coastline, which consists of sand cliffs, is being rapidly cut back, with an erosion rate in the order of 5 m per flooding.

Trustworthy data on the filling of Lake Eyre South are reported for the floodings of 1938, 1955, 1963, 1968, 1973, 1974, 1975, 1976 and 1984. In 1984 Lake Eyre South overflowed to Lake Eyre North. In 1974 water flowed from Lake Eyre North to Lake Eyre South between March and October when an equilibrium level was obtained. Large quantities of salt, estimated at 30 million tons (7.5% of Lake Eyre North content), were transferred into Lake Eyre South during this event, creating, in its lowest portion, a salt crust up to 290 mm thick for the first time on record.

The vast catchment areas of the lakes are only marginally desert and as such are very responsive to even slight variations of rainfall. Considering the long term trends of climatic change is therefore essential. Almost all the non-desert parts of the Lake Eyre Basin area are used for low-intensity grazing of sheep for wool and beef cattle. The very variable rainfall is the most important factor for provision of feed, and low rainfall seasons determine stocking rates. Grazing capacity is directly related to the distribution of artesian wells and excavated tanks. The area of irrigated agriculture is insignificant and restricted to pasture on lands bordering other divisions (l).