Dayet Srji is a shallow seasonal salt lake about 6 kilometres south of Merzouga, appearing after significant winter or spring rains and typically drying to a cracked white pan by early summer. When it fills, it becomes one of the most unexpected sights in Morocco: flamingos — sometimes hundreds of them — wade the shallows against a backdrop of sand dunes and open desert.
The lake is excellent for birding even when the flamingos are absent. It sits on a migratory route and attracts a variety of waders, ducks, and desert birds in the colder months. Bring binoculars: the open ground and flat water allow views of birds from a distance without disturbance.
Whether the lake exists on your visit depends entirely on recent rainfall, which is unpredictable. Ask in Merzouga before making the drive; locals will know. When it is there, the combination of the lake, the dunes rising behind it, and the distant mountains makes for one of the more striking landscapes you will find at this latitude.