Boro - The Okavango Delta in Botswana is one of Africa's natural wonders, but the new Unesco World Heritage Site is facing a multitude of threats, which could lead to its ecological collapse.A canoe slides on the silky surface of the dark water. Between the reeds, water lilies raise their white heads. A golden-coloured heron opens its white wings. A coucal coos in the distance.The visitor to the alluvial fan of the Okavango River in Botswana can also see hippopotamuses raise their backs above the water or herds of elephants cross to an island.Declared one of the Seven Natural Wonders of Africa in 2013 and a Unesco World Heritage Site in June, the Okavango Delta is facing multiple threats to its unique, seasonally evolving ecosystem of waterways, swamps, grasslands and lagoons in the basin of the Kalahari desert.The Okavango, one of three inland deltas in Africa, is nourished by water brought by the river from Angola through Namibia to Botswana. It swells to three times its permanent size of 6 000km2 between May and July after rains upstream.More than 90% of the water evaporates before the rest drains into desert sands or flows into Lake Ngami in north-western Botswana.Concentrations of sand, mud and termite hills give birth to islands that can disappear under water while new ones surface as channels alter their course.Energy"The fact that it is an inland delta in an arid environment makes it particularly sensitive to drying up," said Joseph Mbaiwa, acting deputy director of the Okavango Research Institute in the nearby town of Maun.But other risks are increasing the danger, including climate change, nearby mining, a proposed hydroelectric project in Namibia and poaching. A combination of several of these risks could cause a situation in which "an ecological threshold is crossed and the delta collapses," warned Piotr Wolski, an expert on the delta at the University of Cape Town in South Africa.Mining is not allowed inside the delta, but several companies are prospecting for oil, diamonds and metals in nearby areas.The government has allowed diamond mining in another wildlife area, the Central Kalahari Game Reserve."Eventual mining could produce gases and other types of pollution," Mbaiwa said.Namibia has also long considered building a hydroelectric power station on its section of the Okavango - a plan which, if eventually it were carried out, would hamper sedimentation and erode water channels while reducing the amount of water flowing into the delta, according to experts.Agricultural irrigation in Angola and Namibia is already extracting water from the Okavango while a new study by the University of Cape Town showed that climate change has reduced seasonal flooding."The delta will get smaller," Wolski said.While it is not likely to dry up just because of climate change, "climate change could become a threat when combined with other factors, such as human activity and the strong variation between dry and wet multiyear periods that are typical of Southern Africa," he said.Such a scenario would threaten the Okavango Delta's more than 1 000 plant and nearly 800 animal species, including 482 bird and 89 fish species. Some of its mammals are among the most endangered in the world, such as the cheetah, rhinoceros, wild dog and lion.Break the rulesAbout 150 000 people also live around the delta and have adapted to its constantly changing environment. Villagers for instance live in thatched mud huts instead of brick houses, which are easy to leave and rebuild elsewhere if the delta moves."About a decade ago, when the delta receded, villagers moved deeper inside it" to access fishing grounds, said Oratile Oracle, a farmer who also works as a tourist guide in the village of Boro.Residents, however, also take a toll on the delta. They burn reeds to open the way for fishing and poach buffalo, antelope or giraffe for food.The government tries to combat fires and poaching by sending wildlife officials to educate villagers about their harmful effects. It also keeps tourism in check by limiting the numbers of beds in lodges in the area.The delta attracts tens of thousands of visitors annually, and locals tell stories about visitors injuring hippopotamuses with their motorboats or inadvertently importing foreign plant species."Some tourism companies break the rules by taking more than their quota of tourists and dumping waste into the delta," Mbaiwa said.What is at stake is an unparalleled natural area. As the sun hits its zenith there, the delta quiets. The water is mirror-still. Dark water grass floats near the surface. On one of the islands, a centuries-old baobab tree sheds white flowers while zebras and wildebeest graze in the distance."The delta changes constantly - it is alive," Oracle said. And he hopes it stays that way.