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Human Alterations Contribute to River Flooding, Impact Fish Life

January 24, 2012

By Heather Turner

CORVALLIS, Ore. — All of this flooding isn’t just damaging some homes and yards, but it’s also affecting the fish that live in our rivers.

Oregon State University river ecologists say decades of human alterations on Oregon’s river systems has contributed to worsening the flooding conditions, which they say in turn, can make it difficult for some fish to survive.

What were once complex, braided rivers, with multiple channels that spread the impact of flooding, have been transformed into single channels that act like pipelines.

“We have tried to force the river not to flood, and so we turned it into a pipe, and so as a result we crank up the power,” said OSU River Ecologist Stan Gregory.

For non-native fish like largemouth bass and catfish, the flooding makes it harder to survive.

“They get displaced downstream, they get displaced to the margins and out on the fields and the edges, they may find their way back into the river and back into adequate habitat or they may not,” Gregory said.

However, the floods can be beneficial to native fish like cutthroat trout and steelhead.

With thousands of years to adapt, they’ve learned to swim up tributaries to floodplains, or into farmers’ fields, that can act as a sanctuary.

“The flooded fields, and ditches and all the side channels benefit the fish because they can find shelter from high waters there and food during a period of time when that wouldn’t be available as easily in the main stem of the Willamette River,” said OSU River Ecologist Guillermo Giannico.

OSU river ecologists say human alterations along the Willamette River have caused us to lose 25 percent of the river habitat, 80 percent of the islands, and 80 percent of the area of floodplain forest.

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