UNITED NEWS INTERNATIONAL (UNI) — Fish are washing up dead in one African river.

Scientists say they’re being choked to death by hippo poop.

Around 4,000 hippos are thought to live along the Mara River which stretches across parts of Kenya and Tanzania.

All of these hippos excrete an estimated nine tons of dung every day, which sinks to the bottom of the pools they wade in.

A new study published May 16 in the journal Nature Communications found microbes that break the feces down suck up the oxygen in the hippo pools.

When monsoon rains hit the region during the wet season, these swimming pools/toilets get flushed and the water that the hippos have been stewing in moves downstream.

Researchers say this water that’s now lacking oxygen and full of hippo poop can suffocate large population of fish.

They tested their theory by creating an artificial hippo pool. When they released the soiled water, oxygen levels dropped downstream.