Senegal’s pink lake is on the verge of disappearing — how to protect it

Subject: IR

Section: Msc

Lake Retba:

Lake Retba, also known as Lac Rose, is situated approximately 35km from Dakar, Senegal, and is famous for the pink colour of its waters.
It lies north of the Cap Vert peninsula.
The lake, 6.5 meters below sea level, is separated from the sea by about 1km of dunes.
Its water, primarily sourced from the sea, is highly saline and supports only a few microscopic algae and bacteria.
The Pink Lake is a major tourist attraction in the Dakar region, but its appeal is declining.
Additionally, the lake is a site for artisanal salt mining, involving 1,500 to 3,000 people and producing an estimated 140,000 tonnes of salt annually, distributed nationally and in neighbouring countries.

Why does the water turn pink?

The pink colouration of Lake Retba’s water is due to the presence of the halophilic green algae Dunaliella salina, which thrives in salty environments.
This algae contains red pigments and is often found alongside halophilic bacteria of the genus Halobacterium.
Dunaliellasalina’s ability to withstand high salt concentrations is attributed to its high levels of carotenoid pigments, which protect it from light, and its significant glycerol content.
This algae also contains at least four antioxidant pigments:beta-carotene, astaxanthin, lutein, and zeaxanthin, all of which are rich in vitamins and trace elements.
The lake’s pink hue intensifies when the salinity is high, promoting the proliferation of algae with red pigments, while lower salinity levels favour the growth of other algae with green pigments.

Challenges:

Salt accumulation at Lake Retba is causing significant challenges on both its southern and northern shores.
On the southern shore, the introduction of a drainage channel in August 2022, meant for wastewater and rainwater disposal from nearby suburbs, has led to two major issues: first, the accumulation of solid particles is contributing to the filling in of the lake, and second, the dilution of the lake’s water has resulted in lower salinity. This reduced salinityhinders salt harvesting and is not conducive to the growth of the green alga Dunaliella salina, which requires high salinity for development.
The northern shore faces different challenges. Motorized traffic is threatening the stability of dunes, which are anchored by ageing casuarina trees. The destruction of these trees could lead to the spread of quicksand into the depression. Additionally, the lake’s water supply through the dunes is at risk due to the shallow nature of the aquifers (both fresh and saltwater) and the rapid urbanization in the northern area.
The northern part of the lake features ponds scattered across the area, located where a former channel once connected the lake to the sea. Now filled in by sand from the dunes, the northern part of these ponds has been lost, while the southern part remains.

Source: DTE