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Why are many Eastern Rift lakes salty or alkaline?

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East African mountains and lakes — East African lakes Mountains and lakes of East Africa.

Many lakes in the Eastern Rift are salty or alkaline primarily due to their location in inland troughs at low altitudes, where the environment is hot and dry with high potential for evaporation. Because these lakes often exist in endorheic (closed) drainage basins, water is lost through evaporation and seepage rather than flowing out to the sea, which causes dissolved minerals to concentrate over time.12

The specific chemical composition of these lakes is further influenced by the region's unique geology. For instance, some soda lakes, such as Lake Magadi, receive sodium carbonate (natron) from alkaline waters of deep-seated origin. While many lakes in the Eastern Rift are brackish, exceptions like Lake Baringo and Lake Naivasha remain freshwater, which is believed to be the result of subterranean outlets that allow water and dissolved salts to drain away.1