Nairobi — A natural wonder is happening in Kenya.
Pink flamingos are returning to Lake Nakuru, swooping and wheeling over the water and balancing near sandy shores on their spindly legs.
Over the past eight years, large numbers of these graceful creatures had quit feeding at Nakuru as the lake became polluted by chemicals from a factory and sewage from a growing town nearby. One year the lake almost dried up, leaving huge white pockets of soda dust.
But ''the greatest bird show on earth,'' as it is sometimes called, is back because man has begun to correct his past mistakes.
Thanks to a West German loan, the town of Nakuru has built a modern sewage system. Factory pollution has been brought under control. The town rubbish dump, another factor contributing to the lake's deterioration, has been moved to a site farther away from the water.
''The water situation in the lake now favors the return of the flamingos,'' says game warden Joseph Ayieko.
Mr. Ayieko says there are some half million birds at Lake Nakuru, and ''this number is expected to rise in the next two years.''
At one time there were more than 2 million birds at the lake. They attracted biologists, ornithologists, and tourists from around the world. Flamingo numbers fell to only a few thousand when the lake became polluted.
These strange birds with long necks, masses of pink-tipped feathers, and curved bills live on a diet of blue-green algae. Scientists figure that when Lake Nakuru became polluted, the birds could not easily filter the foreign matter through the specialized machinery in their bills.
If pollution in the lake reached too high a level, they said, the birds would not survive. The birds flew to other lakes in the Kenyan Rift Valley chain where conditions were similar, but not perfect for their lifestyle.
What is special about Lake Nakuru, the thing that seems to make it just right for the flamingos, is its particular combination of saline and alkaline substances, suspended nutrients, freshwater influx from springs, sunlight exposure, and evaporation.
Kenya has also enhanced the flamingos' ecosystem by enlarging Nakuru National Park to 50,000 acres. In addition, nearby farms have been bought up with a gift from the World Wildlife Fund.
Now the visitor can again walk down to the lakeside and stand within a few yards of the flamingos. They slowly, gracefully, tiptoe through the shallows, appearing to survey their world with an air of aristocratic superiority. Then, for no apparent reason, 40 or 50 of them may suddenly take off and wheel around the lake. When they settle again at a more distant point on the shore, they look like a pink carpet.
When the flamingos returned, they were accompanied by pelicans, cormorants, and hornbills.
As the story gets out that the birds are back, spectators are expected to begin to return, too.