The most famous lake is Otjikoto – a black hole near the mining town of Tsumeb, about 450 kilometers north of the capital of Namibia - Windhoek. The lake tapers to a lateral cave system, making it impossible to determine its exact depth, estimated today at 142 feet. Otjikoto provides good visibility, compared to the ocean. It is an isolated reservoir fed mainly by seeping water in which silt brought by the river does not accumulate. As a result, the water in the lake is clear - with 15 meters of visibility on sunny days.

The lake was a weapon dumping ground for retreating German army during the First World War, and the local climate preserved the arms in very good condition. These old artefacts attract divers to Otjikoto, despite the fact that diving in the lake is potentially dangerous, requires special skills acquired during the advanced training, and is not available to the general public. Otjikoto is classified as an underwater museum, therefore it is managed by the Namibian Underwater Federation (NUF) on behalf of the National Monuments Council. Moreover, Otijikoto is considered a national monument and adding or removing anything from the lake is prohibited.

Of interest to divers, besides the sunken weaponry, there are eight different species of fish in the lake, including the critically endangered Tilapia guinasana, which is considered endemic. Otjikoto fish, many of which are brightly colored, attract a lot of attention of researchers investigating this biological curiosity.

• 1. Underground lakes in Namibia