Migrating fish are attracted to the large flows of water coming from Bonneville Dam, and fish-collection facilities along the face of the powerhouse and at each end of the spillway dam use their own flow of water to lead fish into the fishways. The Bradford Island fishway is a long, inclined flume with horizontal weirs that create a series of successive pools, each one foot higher than the adjacent pool downstream, and fish move from one pool to the next higher one by swimming through submerged artifices or over the weir crests. The upper portion of the fishway was recently reconstructed with an inclined series of vertical slots and eddy-like pools instead of the weirs in the lower reaches, a design that biological research has shown is superior for fish passage and allows self-regulating control of water in the fishway. Near the top, the fish pass the counting station and move by the viewing windows.