We also took a sunset cruise on the Zambezi River. Same captain, same boat, same engine issues--but lots of fun! There were lots of small islands in the river just above the falls. There weren't any human inhabitants, just lots of wildlife.
Here is a view of the river with the misty falls in the distance. We found some elephants treading in the water with some hippos closely watching their every move.
Try not to get your tail wet--and keep your snorkel stretched out in front!