But today, a permanent dam barrier not the envisioned natural course of rapids is what keeps sea lamprey at bay.

WSJ: Real Rapids in Grand Rapids?

His colleague, bait-shop owner Josh Smith, proposed modifying the current dam to aid the rapids project but keep the lamprey barrier.

WSJ: Real Rapids in Grand Rapids?

Dr Dario and Dr Stefanini have built him a device called Lampetra (pictured top), which is made of circular segments modelled on the lamprey's cartilaginous vertebrae.

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But opponents believe that the inflatable barrier will not be able to prevent encroachment from the lamprey, a position adopted by the U.S. Fish and Wildlife Administration.

WSJ: Real Rapids in Grand Rapids?

In earlier work, scientists at Northwestern University Medical Center in the US wired a wheeled robot up to a lamprey in a bid to explore novel ways of controlling prosthetics.

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Environmentalists fret that removing dams could increase the risk of flooding and allow invasive fish including the sea lamprey, an eel-like fish with a menacing mouth that attacks other fish to breach the river's tributaries.

WSJ: Real Rapids in Grand Rapids?

Once this had happened, the current could gradually have extruded itself from one of the denser areas of cloud, and followed it as it drifted through space--hanging on, in Dr Benford's words, like a lamprey.

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This one is a fish: a lamprey.

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"We as a country tend to lull ourselves into a false sense of security over the passage of time, " said Andy Lamprey, vice president of the security firm Andrews International and a former Los Angeles Police Department senior SWAT supervisor.

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