Tanzanian wildlife authorities are investigating the deaths of some 10,000 flamingos over the past month at the Lake Manyara National Park.
Only the lesser flamingo species has been affected
Preliminary tests have shown the birds might have died from toxins in algae, the park's chief warden Betty Loibooki told AFP news agency.
Samples have been sent to Germany for further analysis.
Lake Manyara in north-eastern Tanzania is home to over 300 bird species with more than three million flamingos.
"So far it has not yet been established what is exactly causing the deaths; scientists are on the ground to find out," Tanzania National Parks' James Lembeli told BBC News Online.
"The deaths started in mid-June until last week. There have been no more deaths since then," he said.
Two species of flamingos inhabit Lake Manyara - the lesser flamingo, which eats algae, and the greater flamingo, which mainly eats insects.
According to Mr Lembeli it is the lesser flamingos that have been dying over the last month.
Flamingos are an important tourist attraction in Tanzania, second only to lions in popularity.