The Fish River Canyon in Namibia is reputedly the second largest canyon in the world (the largest being the Grand Canyon). There is a lot of debate as to whether or not this is indeed the second largest canyon in the world, most of the arguments seem to hinge on how one actually measures the 'size' of a canyon. Regardless of its ranking in the world of big canyons the Fish River is absolutely magnificent and breathtaking in its immensity. The Fish River Canyon probably formed about 500 million years ago. However it was not only created by water erosion, but through the collapse of the valley bottom due to movements in the earth's crust.