More than 100 hippos in Namibia, including some seen floating on their backs in shallow waterways this week, may have died from an anthrax outbreak that could now affect other species.

Officials say 10 dead hippos were discovered in Bwabwata National Park in northeast Namibia last Sunday, followed by another 99 over the intervening days, per the Namibian.

"Our veterinary services are currently working at the area to determine the cause of death … but the signs so far show that it could be anthrax," Namibia's environment minister says, per the Guardian.

Environment rep Colgar Sikopo tells New Era that an anthrax outbreak "mainly occurs when the level of the river is so low" that it exposes bacteria that can hide in soil for years.

But though anthrax outbreaks aren't unusual in the area, this would appear to be the most significant such event in Bwabwata. While a 2004 outbreak killed at least 180 hippos in Uganda, reports the BBC, previous anthrax outbreaks in Namibia in 2003 and 2004 affected only a small number of hippos and elephants, Sikopo says.

The estimated 109 dead hippos found in the past week represents roughly 8% of Namibia's hippo population, per the Guardian. Sikopo says hippo carcasses are being burned "to prevent further spreading of the disease," if present, and to ensure no person "starts feeding on the meat." Officials warn that crocodiles who've eaten some of the carcasses might already be affected, however.

(Hippos are being killed for their teeth.)

This article originally appeared on Newser: 109 Hippos Turn Up Dead in a Week