In 4000 BCE, a lake Mega Chad larger than all five Great Lakes covered roughly 360,000 sq km of what is now the Sahara. 6,000 years later, only a tiny fraction, well under 1%, of that ancient lake remains

The Sahara that exists today is difficult to associate with a landscape dominated by enormous amounts of water. Yet the region's past was very different. Long before modern records, climate conditions allowed a huge lake to occupy a vast basin in what is now the southern Sahara. Its existence is preserved not in written history, but in shorelines, sediments and scientific reconstructions.

That ancient lake was Palaeolake Mega-Chad. At its largest, it covered roughly 360,000 square kilometres, although some studies have estimated its maximum area at more than 400,000 square kilometres. Even the lower estimate would make it larger than all five North American Great Lakes combined.