Lake Retba, also known as Lac Rose, lies north of the Cap Vert peninsula in Senegal, some 35 km (22 mi) north-east of the capital, Dakar, in northwest Africa. It is named for its pink waters caused by Dunaliella salina algae and is known for its high salt content, up to 40% in some areas. Its colour is usually particularly strong from late January to early March, during the dry season; however, flooding in September 2022 not only disrupted salt harvesting activities on the lake, but because it caused the lake to lose its colour, had a negative effect on tourism.

A pink lake is a lake that has a red or pink colour. This is often caused by the presence of salt-tolerant algae that produces carotenoids, such as Dunaliella salina, usually in conjunction with specific bacteria and archaea, which may vary from lake to lake. The most common archaeon is Halobacterium salinarum.