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The playa and shore of Lake Hart, an endorheic desert lake in South Australia

Salt harvesting in Salar de Uyuni, Bolivia, the world's largest salt flat.

A closeup photograph of salt growths on the crust of a playa lake

A playa; also known as an alkali flat, sabkha, or salt flat; is a dry lakebed, generally the shore of, or a remnant of, an endorheic lake. Such flats consist of fine-grained sediments infused with alkali salts. Their surface is generally very dry, hard and smooth in the summer months, but wet and very soft in the winter months. Playas are small, round depressions in the surface of the ground. A playa lake is formed when rain fills this hole with water, creating a small lake. Playas can also form when the water table intersects the surface and water seeps into them.

Playas are typically formed in semi-arid and arid regions of the world. The largest concentration of playa lakes in the world (nearly 22,000) is on the Southern High Plains of Texas and Eastern New Mexico. While most playa lakes are very small, other examples of playa lakes include Lake Alablab in Suguta, Kenya, and Wild Horse Lake, Oklahoma, USA. Salar de Uyuni in Bolivia, near Potosí, is the largest salt flat in the world at 4,085 square miles (10,582 square km), which is about 25 times bigger than the Bonneville Salt Flats.

Another type of playa is a salina. They are very rare, with only 3 on Earth.^{[citation needed]} A salina flat occurs below sea level, behind a rocky, non-porous beach that salt water can easily penetrate through to mix with fresh water from the ground or other sources.

Many playas contain shallow lakes in the winter, especially during wet years. If the layer of water is thin and is moved around the playa by the wind, an exceedingly hard and smooth surface can develop. Thicker layers of water can result in a "cracked-mud" surface and "teepee" structure desiccation features. Very little water can result in dune formation.

Racetrack Playa is a place in Death Valley National Park, very famous for its 'sailing stones', rocks that mysteriously move across its surface.

While the playa itself will be devoid of vegetation, they are commonly ringed by shadscale, saltbrush and other salt-tolerant plants that provide critical winter fodder for livestock and other herbivores.

In the U.S., playas are important sources of habitat for wildlife, including waterfowl such as ducks and geese, along with sandhill cranes and shorebirds. Amphibians such as frogs, toads, and salamanders also depend on playas, along with various invertebrates such as fairy shrimp. The U.S. playas also play a crucial role to the Ogallala Aquifer, as one of the sole recharging sites for this enormous aquifer.

Threats to playas include pollution from concentrated animal feeding operations such as cattle feedlots and dairies, erosion, fertilizer, pesticide, and sediment runoff from farms, and overgrazing.

Playa areas in Nevada, United States

Playa lake during wet phase - USFWS photo

The extremely flat, smooth, and hard surfaces of playas make them ideal surfaces for motor vehicles and bicycles. Large-sized playas are further excellent spots for pursuing land speed records, as the smoothness of the surface allows low-clearance vehicles to travel very fast without risk of disruption by surface irregularities, and the course of travel does not need to be too precise to avoid obstacles. The playas at Bonneville Salt Flats in Utah and Black Rock Desert in Nevada have both been used for setting land speed records.

The Spanish word playa (IPA: [ˈplaʝa]) literally means "beach". Alkali flats are known by this name in some parts of Mexico and the western United States (pronounced /ˈplaɪə/). On the Llano Estacado and other parts of the Southern High Plains, playa refers to a playa lake, a smaller seasonal depression.

In Arabic, an alkali flat is called a sabkha (also spelled sabkhah,subkha, sometimes sebkha) or shott.

• The Bibliography of Aeolian Research