Like a watercolor in which a brushstroke of dark green has bled into a damp spot on the paper, southern Africa's Okavango River spreads across the pale, parched landscape of northern Botswana to become the lush Okavango Delta. The delta forms where the river empties into a basin in the Kalahari Desert, creating a maze of lagoons, channels, and islands where vegetation flourishes, even in the dry season, and wildlife abounds. April 27, 2009.