Lake Volta was made in the 1960s. Engineers built a huge wall - the Akosombo Dam - across the Volta River. The water backed up behind the dam and slowly filled the valley above it. Over a few years, a brand-new lake the size of a small country appeared on the map.
The lake is about 520 kilometres long - roughly the distance from London to Edinburgh. It covers around 8,500 square kilometres, which is bigger than a country like Cyprus. From space, astronauts can see it clearly as a long, twisting blue shape in the middle of Ghana.
The dam doesn't just make the lake. It also makes electricity. Water rushing through the dam spins giant turbines, which create power for homes, schools and factories all across Ghana - and even for some of its neighbours. Without the dam, lots of people would have no light when the sun went down.
Today, Lake Volta is a busy place. Fishermen go out in wooden canoes to catch tilapia. Ferries cross the lake instead of cars driving the long way around. Tiny islands dot the surface - the tops of hills that became islands when the water rose. People who knew the valley before the lake remember it as a different world entirely.