How rainwater gathers among the dunes
In Brazil’s Lençóis Maranhenses, the dunes are not simply piles of dry sand. The landscape receives heavy seasonal rain, and water collects in the low ground between the hills. Beneath the sand, less-permeable layers help keep some of that water from draining away quickly, allowing shallow lagoons to form.
The dunes shape where the water goes: each hollow becomes a temporary basin. Because the lagoons are fed largely by rain rather than muddy rivers, their water can look remarkably clear against the pale sand.
A landscape on a seasonal clock
The lagoons expand during the rainy months, then shrink as the dry season returns. Sun and evaporation remove water, while some seeps into the ground. Many pools eventually disappear, so the scene is continually remade by the annual shift between wet and dry conditions.
Fish can be found in some of the lagoons when they fill. Their presence reflects the region’s seasonal waters, but the route or survival strategy can vary; it is not safe to assume every fish appears in the same way. As the pools contract, aquatic life faces the same changing conditions as the water itself.
The result is a striking reversal: dunes that seem to promise only sand briefly hold a network of freshwater pools. The lagoons are not permanent features of the desert-like landscape—they are the rainy season made visible.
