This is Scientific Americans 60 Second Science. I'm Jason Goldman.

They weigh about 3,000 pounds and eat about 100 pounds of plants each day.

So your average adult hippo produces quite a lot of poop. By some

estimates a single hippo blasts out more than 10 pounds of waste each day.

And all that hippodung gets mixed into the ponds and streams where they spend most of their

time.

We generally think of this process as beneficial, an ecosystem service, a way for nutrients

to flow from terrestrial stream-side ecosystems into the water itself.

Their dung is a sort of fertilizer for aquatic life.

And all of that is true, at least when water moves from pond to pond.

At one time, many African waterways continued to flow even during the dry season.

But people have diverted lots of that water for agriculture.

So now Tanzania's great Ruaha River stops flowing during the dry season, leaving behind a series

of stagnant pools in which the hippos keep on pooping.

Especially in these high density pools at the peak of the dry season there's a huge buildup of dung.

So we ended up just pulling out these nets that I have no fish but are just filled with hippo dung.

University of California Santa Barbara ecologist Keenan Steers.

Unable to wash down river, the nutrients build up while dissolved oxygen in the water decreases.

And changes in the chemistry can influence biodiversity within these pools as well.

So specifically fish as well as aquatic invertebrates.

Only a few types of fish can survive in these oxygen-poor aquatic environments for more than a few weeks.

It's bad news for biodiversity, but it's also deleterious for the dinner plate.

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