Lake Volta
Ghana · built 1965
Lake Volta (Lac Volta), the largest artificial reservoir in the world based on surface area, is contained behind the Akosombo Dam which generates a substantial amount of Ghana's electricity. It is completely within the country of Ghana and has a surface area of 8,502 square kilometres (3, 283 sq mi). It extends from Akosombo in the south to the northern part of the country.
Reservoir data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).