Barriers to Fish Migration When it comes to fish migration, most people’s thoughts turn immediately to Atlantic salmon leaping over waterfalls on their way to the headwaters to spawn. However, nearly all river fish migrate to some degree and for various reasons. The ability to do move freely up and down a river system is therefore essential for healthy fish populations. When the Foundation started in 1996, large areas of the Wye and Usk catchments had become blocked to migrating fish. The majority of these barriers were on tributaries. As a result, the biggest negative impact was on salmon and trout who use the smaller streams to spawn. Read more about barriers to migration and the Foundation’s work to restore access.