Complex sentence: Lake Volta (located at) is the largest reservoir by surface area in the world, and the fourth largest by volume, lying in Ghana and covering almost 8,502 km² (3,275 square miles).
Split into simpler sentences: Lake Volta (located at) is the largest reservoir by surface area in the world, and the fourth largest one by water volume. It is located completely within the country of Ghana, and it has a surface area of about 8,502 km² (3,275 square miles).