Birds are the first to arrive in any numbers, wattled cranes, then black storks. Behind the birds come buffalo. After weeks of marching, their trek is coming to an end. As the water sweeps into the Okavango, a vast area of the Kalahari has transformed into a fertile paradise. Nowhere on our planet is the life-giving power of water so clearly demonstrated. The Okavango becomes crisscrossed with trails as animals move into its heart. The new arrivals open up paths like arteries along which water flows, extending the reach of the flood.