Every year, between February and April, the rains turn the Barotse Floodplain - a huge flat grassland - into a giant lake. The villages there are on slightly raised mounds, so the people stay safe. But when the water gets too high to live with comfortably, they all move - together - to a second village built on dry ground at the edge of the floodplain.
The most spectacular part is the journey of the Litunga (the Lozi king). He travels in a long royal barge called the 'Nalikwanda', painted with black and white stripes, with a model of an elephant on top. Around 100 paddlers in matching uniforms power the canoe. Behind him, hundreds of smaller canoes follow - all paddling together across the water.
The whole journey takes around six hours. People sing, drum, cheer and clap from the banks. Other canoes carry the queen, the royal household, drummers, even cooks. When the king arrives at his dry-season palace, there is a big celebration with traditional dance, music and food.
Kuomboka has been celebrated for hundreds of years, since before any Europeans came to Africa. It is one of the oldest and most loved traditions in southern Africa. Schools in Western Province sometimes give children the day off to take part - and people travel from all over Zambia (and the world) to watch.