Where do the rapids, put-ins and bridges come from?

From OpenStreetMap: rapids (with their whitewater grade where it is mapped, shown as Class III and so on), slipways, canoe put-ins and take-outs, fishing access sites, bridges where they cross the river, dams, weirs and falls. Some rivers are mapped in great detail and some hardly at all. The builder places every name for you, and in the Studio each one becomes ordinary text: rename a pool the way your guide calls it, add the runs nobody mapped, or delete what you do not want.