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Lake Retba of Senegal
Lake Retba, situated in Senegal, West Africa, is a bright pink body of water also referred to as Lac Rose or the Pink Lake. The lake’s distinctive color is a result of the proliferation of Dunaliella salina, a halophilic green algae containing protective red pigments.
Location and Geography of Lake Retba
Lake Retba, also referred to as Lac Rose or the Pink Lake, is situated approximately 35 km from the city of Dakar, capital of Senegal in West Africa. It lies in a natural depression with its shoreline 6.5 meters below sea level. The lake is encircled by sand dunes that provide isolation from the nearby Atlantic Ocean, located about 1 km away.
The sea is connected to Lake Retba via subterranean freshwater and saltwater aquifers that run through the dunes at higher elevation. These aquifers supply the majority of the water and salt content to Lac Rose . So despite being a landlocked body of water, the Atlantic Ocean plays a vital role in sustaining both the salinity and pink coloration caused by salt-loving microorganisms.
The sand dunes are stabilised by casuarina trees, a protective barrier that prevents potential quicksand encroachment into the vulnerable Lake Retba depression. Maintaining dune integrity through preservation of this vegetation is critical to prevent flooding of the lake basin and collapse of lake ecology.
Why the Lake Retba water is Pink?
The pink coloration of Lake Retba is due to Dunaliella salina, a type of halophilic green algae that proliferates in the lake. Under stressful conditions like intense sunlight and high salinity, these algae produce protective red pigments such as beta-carotene. The pigments are carotenoids that serve as antioxidants.
Lake Retba’s waters tend to be pinkest during Senegal’s dry season, between November and June. This period has both abundant sunlight as well as high concentrations of salt, prompting the algae to generate increased amounts of pigments. The salinity becomes particularly elevated as water evaporates in the heat, providing prime conditions for pigment production.
Seasonal Changes
The vibrant pink color of Lake Retba fades and dulls during Senegal’s annual wet season, which spans July to October. The increased rainfall during this period causes decreased salinity in the lake as the waters become freshened by periodic inflows. Greater cloud cover also means less intense sunlight reaches the lake. Together, these wet season conditions create an environment less ideal for pigment production by the Dunaliella salina algae that impart the rosy hue.
Concentrations drop of orange and red beta-carotene pigments that protect the algae under high salinity and sunlight exposure. The lake only regains its pinkness during the ensuing annual dry season as waters evaporate, salinity rises dramatically, and sunlight bathes the lake.
What are the environmental threats faced by Lake Retba?
Lake Retba currently faces multiple environmental threats that could lead to its disappearance. Pollution from nearby hotel development and rapid urbanization is flowing into the lake, resulting in extremely high nitrate levels up to 15 times the safe limit for drinking water set by WHO.
Mining of protective barriers like shell middens and dune sand destabilizes the terrain and landscape surrounding the lake. Additionally, excessive and unchecked salt harvesting over many years could allow salts to accumulate and the lake to eventually fill in. Finally, the loss of stabilizing casuarina trees anchoring the neighboring dunes poses the risk of encroaching quicksand into the Lake Retba depression.
Additional dangers stem from the dumping of wastewater and solid particles via an artificial drainage channel, threatening to accelerate sedimentation and reduce salinity. Motorized traffic on the fragile dunes by the lake further endangers their stability. Together, these multiple threats jeopardize the future of both the vibrant pink lake itself as well as the local communities dependent on it for tourism and salt production.
Salt Production
Lake Retba provides essential income to over 1,500 local salt harvesters who extract minerals from its very saline waters. The annual production of salt at the site reaches around 140,000 metric tons. This salt is primarily used for cooking, food preservation, and consumption within Senegal, while a portion is exported to neighboring African countries as well.
Protecting the ecological viability of Lac Rose is thus crucial not just for its biodiversity and tourist appeal, but also to ensure sustainable livelihoods and economic activity focused on a traditional industry tailored to the regional climate and geography.
Experts Recommendations to save Lake Reteba
To preserve Lake Retba, a series of measures have been advanced. Banning the destruction of natural land barriers like shell middens, regulating nearby construction and land use, rehabilitating stabilizing vegetation like the casuarina trees that anchor the adjacent sand dunes, and implementing an integrated management plan have been put forward. These propose to control threats from pollution, flooding, and encroaching sands.
Additionally, Lac Rose constitutes a major tourist destination, attracting visitors wishing to float in its buoyant saline waters tinted pink by algae. At the same time, salt harvesting supports 1,500-3,000 local workers, with annual production reaching 140,000 tons for domestic markets and export across African countries. Protecting the pink lake would ensure the persistence of these additional economic and recreational benefits.
