Botswana’s Okavango Delta, a 22,000 square- kilometer unending maze of wetlands surrounded by the Kalahari Desert, is one of the last untouched refuges for wildlife on the planet, showing visitors “what the world used to be without us,” says conservation biologist Steve Boyes. It cannot survive the loss of any freshwater arteries. Into the Okavango chronicles Boyes’ trip down the headwaters of Angola’s keystone Cuito River into the delta. Perhaps his team’s biggest discovery is that the peat bogs into which the Cuito seems to disappear hold enough water to supply the Delta with the 2.5 trillion gallons it needs annually. But even this secret reservoir can’t guarantee protection of the endangered Delta from human impacts.