black-water raftingˌblack-water ˈrafting noun [uncountable] 
the activity of riding in an inner tube (=large rubber tube filled with air, like those inside a tyre) along a fast-flowing river that runs under the ground through caves
the activity of riding in an inner tube (=large rubber tube filled with air, like those inside a tyre) along a fast-flowing river that runs under the ground through caves