To free salmon stuck behind dams in Oregon’s Willamette River Valley, here’s what the U.S. Army Corps of Engineers has in mind:

Build a floating vacuum the size of a football field with enough pumps to suck up a small river. Capture tiny young salmon in the vacuum’s mouth and flush them into massive storage tanks. Then load the fish onto trucks, drive them downstream and dump them back into the water. An enormous fish collector like this costs up to $450 million, and nothing of its scale has ever been tested.

The fish collectors are the biggest element of the Army Corps’ $1.9 billion plan to keep the salmon from going extinct.

The Corps says its devices will work. A cheaper alternative — halting dam operations so fish can pass — would create widespread harm to hydroelectric customers, boaters and farmers, the agency contends.