From the Introduction:
Every once in a while, after several years with exceptionally heavy and long rain periods the plains turn into a shallow lake. Often again for years at a time. The local fauna has long since adapted to this cycle and while the plains are usually overgrown with long grass, even longer reeds and water lilies spring up as soon as the ground is covered by water. The lake itself is shallow. And before long fish, displaced from small rivers overflowing their banks start to spread. The lake itself is quite shallow. Even at its deepest spots an adult could stand upright without having to actually swim. Still the locals have developed simple bamboo rafts that allow them navigate this shallow body of water without difficulty to make the best use of this temporary source of food. Before long the lake disappears again, almost as fast as it appeared, after a few years where the rain showers could not quite compensate for the water evaporating from the lake.