World Facts

The Poisonous Lake of Tanzania

The over-saturation of natron and trona have combined to make this lake unlike any other.

Where is Lake Natron?

Lake Natron is located in the Arusha region of Northern Tanzania. Natron is a soda and salty water lake very close to the Kenyan border in the Gregory Rift, which is the Eastern part of the East Africa Rift.

Primarily, the lake is fed by the Ewaso Ng’iro River, which originates from the central region of Kenya and by springs that are rich in minerals. The river itself is not that big nor is it deep. The river has a depth of fewer than 10 feet with a varying width depending on the level of water.

Natron itself has a maximum width of 22 kilometres and a length of 57 kilometres. The region around the lake does not receive much rainfall with irregular seasonal rains a common occurrence. If the rains come, it’s typically between May and December averaging around 800 millimeters annually with the scorching sun frequently raising the temperatures above 104⁰ Fahrenheit.

Why is Lake Natron Considered to be a "Poisonous Lake"?

The poison of the lake is brought about by the high temperatures which, incidentally, are why the lake is called Natron. The high temperatures have caused high evaporation levels of the water from the lake. As a result, a material called Natron is left behind. Natron’s scientific name is sodium carbonate decahydrate. Another residue left behind is sodium sesquicarbonate dehydrate, which is otherwise known as trona. These two substances are very basic and raise the pH levels of the lake to more than 12. As if this is not enough, the bedrock of the lake is made up of highly alkaline trachyte volcanic material that has high levels of sodium. All these materials have been there since Pleistocene times. The significant levels of carbonate found in the lava and the relatively low levels of magnesium and calcium have allowed the formation of a caustic alkaline brine.

Majority of the fauna (animals) cannot tolerate, much less survive, the high temperatures or salinity of the water. That is not to mean that there are no animals. Some invertebrates and birds live around the lake. Some fish can survive close to the edge of the lake where it is less saline. The area around is also the only regular breeding grounds for lesser flamingoes who in East Africa are classified as “near-threatened.”

Which Animals Can Live in Lake Natron?

The lake’s color is characteristic of areas where there are high rates of evaporation. As a result, during the dry season, salinity levels rise and salt-loving organisms begin to thrive. Such kinds of organisms that thrive in these conditions include some type of cyanobacteria that make food and nutrients through photosynthesis as other plants normally do. The cyanobacteria contain a reddish pigment responsible for photosynthesis. This pigment is the one responsible for making the center of the lake a deep red color, while the shallower parts are orange. There are other micro-organisms that live on the crust of the lake that also give the red and orange color.

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