Namibia’s Bottomless Lakes – Otjikoto & Guinas

Excerpt from Amy Schoeman’s Notes on Nature

With its emerald green water and the effervescent light filtering through the vegetation on its rim, Otjikoto Lake exudes a mystical quality that lives up to the legend and folklore that surround it to this day. To the north-west lies its sister lake, Guinas, noted for its scenic setting and the ink-blue colour of its water.

In as far back as 1851, the explorers Galton and Andersson measured Otjikoto’s depth as 55 metres, an accurate assessment, as was proved by subsequent plumbings. Yet the notion still persists that Otjikoto and its sister lake Guinas are bottomless, that it is perilous to swim in them, as there are strong undercurrents, and that the two lakes are linked by subterranean passages.

Despite evidence to the contrary, people prefer to believe that the two sinkholes are enigmatic phenomena that cannot be accounted for scientifically, today as much as when the two explorers first encountered them. Even after Galton, Andersson and their fellow explorer, Allen, had stripped, dived in, swum around and climbed out unharmed, the onlooking Bushmen and Wambos held fast to the belief that no living creature that entered the water ever came out alive again.

An unfortunate occurrence that lent durability to the myth was the drowning in 1927 of Johannes Cook, postmaster of Tsumeb, who dived off the rocks and disappeared without a trace. The shape of the lake, rather like an upside-down mushroom, explains why his body was never recovered. He probably tried to surface under an overhang and was then knocked unconscious. These same overhangs prevented his body from rising to the surface.

In 1915 Lake Otjikoto’s reputation of being bottomless possibly led to the dumping of a considerable supply of artillery and ammunition into its murky depths by retreating Schutztruppe, rather than let the armaments fall into the hands of the South African troops. The latter, however, in co-operation with the Department of Public Works, recovered a number of guns and large quantities of ammunition by using grappling hooks, which were later put to use in the East African campaign.

Divers have subsequently, in co-operation with the Windhoek State Museum, managed to salvage some of the equipment, among other things an ammunition wagon still in perfect condition, which was painted and displayed in the Alte Feste Museum in Windhoek.

The emerald green water of the Otjikoto Lake

HOW WERE THE TWO LAKES FORMED?

Otjikoto and Guinas lie in the Otavi mountain land, which consists of a thick succession of well-stratified dolomite and limestone, estimated to be about 700 million years old. The present landscape originated by gradual long-lasting erosion of an originally even thicker mass of dolomite or limestone.

These rocks, being carbonates of calcium and magnesium, are soluble in water, especially if they contain some carbon dioxide. Large masses of carbonate rocks such as the Otavi Mountains, Southern Transvaal, Yugoslavia and the Alps, are criss-crossed by a system of solution channels which have generally developed on joints, fracture zones, or bedding planes. These are partially filled with ground water.

Extensive cavities can originate in the hard rock, of which the Cango Caves in South Africa are a good example. At the same time the whole rock mass is gradually eroded, and now and then big cavities are exposed by weathering, or the roof caves in when it has become very thin. This is the case with Otjikoto and Guinas. Thin solution channels lead away from them, although the two lakes need not necessarily be directly connected. The lakes are fed by water seeping through porous rock from southern Owambo.

At the water surface Otjikoto has a diameter of about 100 m and a depth of 55 m, as plumbed by Galton many years ago. With a depth of approximately 100 m, Guinas is much deeper. It has a similar upside-down mushroom shape as Otjikoto, with a spectacular underwater cave under one of its overhangs, in which there are stalagmites and stalactites, formed when the lake had a lower surface level.

Suggestions that the two lakes are linked by underground passages are unfounded, as there is about 8 m difference in the surface levels, Otjikoto being the lower of the two. On occasions when the level of one or the other has risen because of good rains in the catchment area, the other has remained at the same level.

Halfway between Tsumeb and Grootfontein is the largest subterranean lake in the world. It is called Dragon’s Breath, has roughly the size of two rugby fields, and is situated 100 m underneath the ground. This lake is “bottomless” in the sense that because of its slanting cylindrical shape, it has been impossible to measure its depth accurately. Because of its situation, however, within a hill with its mouth at the crest and very steep walls down to the water surface, access is difficult.

 THE FISHES OF GUINAS AND OTJIKOTO

The two lakes are populated by fish that are biologically quite remarkable. An unusual species of dwarf bream, Pseudocrenolabrus philander dispersus, occurs in small numbers in the lower strata of both lakes. The interesting aspect of this fish is that it breeds in its mouth. Instead of constructing a nest, the female carries the eggs and fry around in her mouth.

Normally the dwarf bream is a shallow-water fish, but in Otjikoto and Guinas it has somehow adapted to live and breed at the bottom, while large populations of a nest-building bream, Tilapia guinasana, inhabit the higher strata of the lakes. This nest-building cichlid, because it has no predators, multiplied up till recently into thousands, especially in Otjikoto. A count done by the State Museum in the early seventies estimated that there were at least 268 000 in Otjikoto alone.

Also known as Otjikoto tilapia, these fish are unable to nest at the bottom of the lake, as this is beyond their survival depth, and they consequently utilise every available nook and cranny in the walls higher up. They are colourful fish, ranging from white to green, grey and dark blue, and even striped varieties, some of which are bright yellow with black stripes. Their supremacy in Otjikoto came to an abrupt when kurper were unwittingly introduced into the lake. Feeding on the tilapia, the kurper increased rapidly, while the tilapia are now estimated to be less than 20 000 and in danger of being wiped out completely by the newcomers.

 USES OF THE LAKES

Otjikoto has been a popular tourist attraction since its discovery. Over the years its waters have been used for mining, irrigation and, in the sixties, for the construction of a road to Owambo. At present the water is pumped regularly by TCL to irrigate their plantation, which causes its level to sink between 1.5 and 2 m during the week when pumping.

Lake Guinas is situated on a farm and is therefore less accessible, although it can be viewed after obtaining the farmer’s permission.

An aspect of Otjikoto which is particularly distressing is the collection of between 5 and 10 tons of tins, bottles, barbed wire and other rubbish that has been thrown into its depths over the years. It would take a major project for a diving team, which would be costly and time-consuming, to clean it up properly.

Acknowledgements

To Theo Schoeman for pointers and background information and to Dr KEL Schalk, Geological Survey, for information on the geological origin of the lakes.

Bibliography

“Otjikoto Lake” by MJ Penrith as published in SWA Annual 1978

Discover Namibia by Michael Brittan