Lençóis Maranhenses National Park

Lençóis Maranhenses National Park is located in Maranhão state in northeastern Brazil, just east of the Baía de São José. The protected area of 155,000 ha (380,000 acres) includes 70 km (43 mi) of the Atlantic coastline and an interior of rolling dunes.

The sand is carried to the park from the continent's interior by the Parnaíba and Preguiças rivers, where it is then driven back inland up to 50 km (31 mi) by winds, creating a series of dunes rising as much as 40 m (130 ft) tall.

While much of Lençóis Maranhenses National Park has the appearance of a desert, the area receives about 1,200 mm (47 in) of rain per year. In contrast, deserts, by definition, receive less than 250 mm (10 in) annually. About 70% of this rainfall occurs between January and May.

During the rainy season, between January and June, the rainstorms fill the spaces among the dunes with freshwater lagoons of up to 100 m (330 ft) in length and 3 m (10 ft) in depth and together comprising as much as 41% of the area of the park. The water in the lagoons is prevented from draining by a layer of impermeable rock beneath the sandy surface.

The area of the park has an average annual temperature of between 26°C (79°F) and 28.5°C (83.3°F) and an annual temperature variation of about 1.1°C (2°F).

The lagoons typically have a temperature between 27.5 °C (81.5 °F) and 32 °C (90 °F), a pH of between 4.9 and 6.2, and low levels of dissolved nutrients. When the dry season returns, the pools quickly evaporate, losing as much as 1 m (3 ft) depth per month.

The park's lagoons are often interconnected with one another and the rivers that run through the area. As a result, they are home to some fish and insect species, including the wolf fish, which burrow down into wet layers of mud and remain dormant during the dry season.

In the park's interior, two oases or restingas are located: Queimada do Britos, covering an area of 1,100 ha (2,700 acres) and Baixa Grande, covering an area of 850 ha (2,100 acres).

Besides the dunes that form the park's centerpiece, the ecosystem includes restinga and mangrove ecosystems.

Lençóis Maranhenses National Park is home to four species listed as endangered, the scarlet ibis (Eudocimus ruber), the neotropical otter (Lontra longicaudis), the oncilla (Leopardus tigrinus) and the West Indian manatee (Trichechus manatus). The park also includes 133 species of plants, 112 species of birds, and at least 42 species of reptiles.

In 2017, Lençóis Maranhenses National Park was added to the UNESCO World Heritage Tentative List due to its natural significance.