that's just the game being buggy with the draw distance boundries, it seems to like to divide stuff with rivers at places. I've had the same happen with weapon scopes, and as I moved closer to the river you'd see the deer fall out of the sky from about 1.5 meters high to the ground. I've used the refined bincos from one of the peaks on the south west side of the heartlands/emerald area and seen marks all the way up in the marsh .