The fence has not kept out the outside world. The National Park, even when first set up, was less than a mile from the town of Nakuru the fourth largest in the country - and it has now expanded to within yards of the fence. Sewage and industrial effluents have flowed into the lake, as have soil, pesticides and fertilisers from farmland. Flamingos have been poisoned, tens of thousands have died.
If the park's wildlife is to be conserved, the environmental and economic conditions of the entire region have to be addressed, and the people of the area have to be convinced of its value. WWF has a programme designed to do this, helping farmers in the region to plant trees, construct terraces for soil conservation, assisting local people in developing environmentally- friendly enterprises like beekeeping, garbage disposal and controls on industries in Nakuru town. There is a long way to go, but it has scored several successes - last year more than 140,000 trees were planted and the flow of sewage into the lake was finally stopped due to Japanese aid.
Designating a national park does not automatically ensure its protection. By 1992 an official tally listed over 100 protected areas worldwide as at risk; but the list was then abandoned because "nearly every protected area and park in the world is threatened to some extent". The best security for reserves - and for wildlife in general - is if they enjoy the support of the local people, which is best obtained, particularly in developing countries, if they benefit from it economically. But in the past areas were often protected almost in defiance of them, as they were kept out of areas where they used to hunt or graze their livestock and their own animals and sometimes their own lives were threatened by the wild animals.
But WWF has been pioneering an entirely different approach - working with the local people - for at least the last 15 years.
In Namibia, under South African rule, wildlife protection efforts generally excluded local people and alienated them; they did little to stop the flourishing poachers because they felt they had no interest in doing so. But a project in the far North-west of the country did start including them and the numbers of rhino and elephant doubled. After independence in 1990, the government with WWF's help made the new approach national policy. People are given the rights to their own wildlife resources, and benefit from them through local tourism projects, through harvesting grasses and other products, and even through selling licences to trophy hunters to kill limited numbers of now abundant animals.
In Brazil, WWF is working with the people in one of the most remarkable places in the world - the flooded forest of the Amazon, an area the size of Switzerland which is under water for six months of the year and is a vital nursery for fish as well as a unique wildlife area. Some parts of it have been set aside for complete protection, others for local fishing, while others still can be fished commercially. Communities will take responsibility for areas near their villages, provide park rangers, and make sure the system is working properly.
The Korup National Park, Cameroon - mainland Africa's richest rainforest, and an important WWF project - is surrounded by a buffer zone in which local people are encouraged to make an income from improved agriculture, trades for example carpentry, livestock and the sustainable harvesting of forest products. There is also some small-scale timber extraction, all of these in the buffer zone.
In neighbouring Nigeria, WWF encouraged the local Fulani people to stay in enclaves the Gashaka Gumti national park when it was formed and is now brokering agreements between them and park authorities for managing these areas.
And in India it is working with UNICEF on managing water resources to preserve both the environment and the health of children.