When the dam was built, the river slowly backed up behind it and filled a long valley. It took about five years to fill completely. The result is one of the largest man-made lakes in the world. From space, Lake Kariba looks like a long blue worm wriggling along the border.
Kariba Dam itself is a giant curved concrete wall, 128 metres tall. Water flowing through it spins enormous turbines that make electricity - enough for millions of homes in both Zambia and Zimbabwe. The two countries share the lake and the power evenly.
Dead trees still stand in the lake in some places, where the old forest never rotted away. They are called 'petrified trees' and create a strange forest under the water surface, perfect for fish to hide among. Tiger fish, bream and Kapenta (a small silver fish about the size of a sardine) live here in huge numbers.
People who live around Lake Kariba fish for Kapenta at night, in special boats with bright lights. The Kapenta swim up towards the lights, thinking they are the moon, and the fishermen catch them in nets. The dried Kapenta is eaten all over southern Africa - it tastes salty and crunchy.