It released an overlay of photographs taken by one of its Earth observation satellites, Envisat, on 1 July 2006 and 6 July 2009.

Once the world’s fourth-largest inland body of water but now a byword for ecological calamity, the Aral Sea has been retreating over the last half-century after rivers that fed it were diverted for Soviet cotton irrigation projects.

Around two decades ago, it split into the Small Aral Sea in the north, located in Kazakhstan, and the Large Aral Sea, shared by Kazakhstan and Uzbekistan.

The horseshoe-shaped Large Aral Sea began to split into eastern and western lobes, in 2000.

"The eastern lobe retreated substantially between 2006 and 2009," ESA said in a press release.

"It appears to have lost about 80% of its water since the 2006 (image) acquisition, at which time the eastern lobe had a length of about 150 kilometres (93 miles) and a width of about 70 kms (43 miles)."

The Large Aral Sea is expected to dry out completely by 2020, it added.

Efforts are underway to save the far smaller northern part, thanks to the Kok-Aral dike, a project of the World Bank and Kazakhstan government.

Since the barrier was completed in 2005, water level in the northern section has risen by four metres (13 feet).

The desiccation of the Aral Sea is considered by some experts to be the worst man-made ecological catastrophe ever, but one that also has had huge implications for human wellbeing.

Fishing and other shoreline industries that once thrived have been destroyed. Each year, tens of thousands of tons of salt-laced dust blow from the dried-up seabed, much of it contaminated by pesticides, affecting health.