 The name &ldquo;Lençóis de Maranhenses&rdquo; (literally, the sheets of the people of the Maranhão) refers to what looks like white sheets drying in the sun; their folds, moved by the wind, settle into curves so typical for sand deserts. Located just outside the Amazon Basin, the region is subject to a regular rain season. Fresh water collects in the valleys between sand dunes and is prevented from percolating down by a layer of impermeable rock that lies underneath the sand. This results in blue, green and black fresh water lagoons of up to 100 metres diameter, surrounded by desert-like sand. 