Sir David Attenborough has joined environmentalists in condemning a $250 million plan by Tata, the Indian conglomerate, to build a soda ash plant on a lake in eastern Africa that is home to a million endangered Lesser Flamingos.

The naturalist and broadcaster said the development, due to be considered by Tanzania’s environment minister today, would be “an ecological disaster” and would deliver a “huge blow” to the $2bn-a-year tourism industry in the region.

Tata Chemicals, through a joint venture with the Tanzanian government, wants to extract sodium carbonate, whose trade name is soda ash, from Lake Natron, one of the world's few natural deposits of the chemical used in the making of glass, detergents and soaps.

The project, involving a plant, a coal-fired power station, transport links and housing for more than 1,200 construction workers, would consolidate Tata’s global position at as the third biggest soda ash manufacturer.

However, it also threatens “the greatest ornithological spectacle in the world”, according to wildlife experts, who say the lakes in the Rift Valley near the Kenyan border provide the only reliable breeding ground for 1.5 million to 2.5 million Lesser Flamingos. East Africa accounts for three-quarters of the global population.

They say the plant – pumping 550 cubic metres of brine per hour and producing 500,000 tonnes of soda ash a year - would alter the alkaline lake’s chemical balance, destroying the spirulina, a type of bacteria on which the flamingos feed, giving them their distinct rose-pink plumage. It will also disrupt the lives surrounding of nomadic Masai communities.

“Lake Natron’s vast flocks of shimmering pink flamingos are one of the world’s greatest wildlife attractions. These spectacular birds deserve the strongest protection we can offer them,” Sir David said.

“Any threat to their future would not only be an ecological disaster, it would deal a huge blow to tourism in east Africa which helps ensure the survival of the region’s spectacular wildlife and wild places.”

The sight of millions of Lesser Flamingos - the smallest of the six flamingo species - migrating between lakes is a big tourist attraction. It is worth $500,000 a year to the local economy, according to opponents of the plant.

The leaders of conservation groups in 23 African countries have signed a petition urging Mark Mwandosya, Tanzania’s environment minister, to reject the proposal.

Graham Wynne, chief executive of the Royal Society for the Protection of Birds, said: “These birds are incredibly fragile and this is the one lake left where they breed. They start in this lake or not at all. There is no reason on earth to allow this ill-conceived project. The economics are weak and the implications for wildlife and the environment are deeply depressing.”

Lake Natron Resources, the joint venture company, has submitted a revised version of its proposal after carrying out an independent environmental impact assessment.

Tata Chemicals produces almost 3 million tonnes of soda ash a year, half of which comes from Brunner Mond, its UK-based subsidiary that owns Kenya’s Laka Magadi, another natural source.

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