When salmon make their way back upstream to spawn, they can encounter a number of manmade barriers, such as dams and locks. To ensure the fish can progress, humans have built stepped channels that go over or around the obstructions. Known as fish ladders these help the salmon overcome otherwise impassable obstacles and carry on the rest of their perilous journey. The most common type of fish ladder looks like a long staircase of mini waterfalls up which the fish can leap, but other varieties include elevators, pools-and-weirs and baffles.
The Bonneville Dam on the Columbia River is a major salmon thoroughfare from the Pacific to freshwater spawning areas between Oregon and Washington. Hundreds of thousands of salmon take this route every year so the addition of the Bonneville fish ladder means these aquatic commuters can get where they need to go.