Officials from Botswana say they have solved the mystery of mass deaths of elephants earlier this year. The hundreds of elephants died from ingesting toxins produced by cyanobacteria.

Government officials add they will be testing waterholes for algal blooms next rainy season to reduce the risk of another mass die-off.

The mysterious death of 350 elephants in the Okavango delta between May and June had made researchers suggest they were killed by a rodent virus known as EMC (encephalomyocarditis) or toxins from algal blooms.

But their latest tests have detected cyanobacterial neurotoxins to be the cause of deaths. These are bacteria found in water.

Toxins were initially ruled out because no other species died. But scientists now think elephants could be particularly susceptible because they spend a lot of time bathing and drinking large quantities of water.

Local sources suggest 70% of elephants died near water holes containing algal blooms, which can produce toxic microscopic organisms called cyanobacteria.

Climate change is increasing both the intensity and severity of harmful algal blooms, making this issue more likely to reoccur. In July, the government’s official count was 281 deaths but this has now risen to 330 deaths.