This is scientific Americans 62nd Science.

I'm Jason Goldman.

In the early 19th century, the fur industry

reached what was then known as the Oregon Territories.

Lewis and Clark found massive numbers of Pacific salmon and steelhead trout there,

swimming among the Beaver dams scattered across the Columbia River Basin.

But in an effort to starve American interests, Canada's Hudson's Bay Company tried to create a fur desert by killing off as many fur-bearing animals as they could. As a result, beavers had all but disappeared from the area by the year 1900,

and once the beavers and their dams were gone, fish populations dropped.

Today, steelhead trout numbers in the region continue to fall, but scientists and government agencies are working to restore their habitats.

We're looking for restoration approaches in these areas to recover ESA listed species, but we really don't know what works and what doesn't.

Nick Bowers of the environmental consulting firm Ecological Research and Utah State University.

He says that the U.S. spends a billion dollars each year to restore watersheds, but without any real empirical information to guide those efforts.

So Bowers and his team tested the idea that by helping beavers they could help the fish.

Dams naturally alter the flow of streams, providing fish with a variety of suitable habitats,

but the watersheds have become so degraded that there's not enough woody vegetation available for the beavers to build

strong dams.

The flimsy ones they do build get washed away whenever there's a big storm.

The idea was can we reinforce these dams so that they maintain their integrity during high flows and can be maintained by beavers to capture this sediment to reconnect that floodplain.

For seven years the researchers compared bridge creek. of the

floodplain. For seven years the researchers compared Bridge Creek, which had lots of artificially strengthened dams,

to Murderer's Creek, which had none.

And in Bridge Creek, the fish flourished,

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