Lençóis Maranhenses National Park is an area of low, flat, occasionally flooded land, overlaid with large, discrete sand dunes. It encompasses roughly 1.500 km2, and despite abundant rain, supports almost no vegetation.

Composed of large, white, sweeping dunes, at first glance Lençóis Maranhenses looks like an archetypal desert, but in fact it is not an actual desert. Lying just outside the Amazon Basin, the region is subject to a regular rain season during the beginning of the year.

The rains cause a peculiar phenomenon: fresh water collects in the valleys between sand dunes and is prevented from percolating down by a laeyer of impermeable rock which lies underneath the sand. The resulting blue, green and black “lagoons” are surrounded by the desert-like sand, and reach their fullest between July and September.

The national park status serves only as a means of protecting the area’s ecology; consequently many people reside in the park, as is also the case with nearby Jericoacoara. The inhabitants work primarily as fishermen.