Rapids are fast-flowing stretches of white water formed where the river surface breaks up into waves because rocks are near to the surface. The rocks are usually not level but slope down into the ground.

Rapids show as white water on this river. Notice the rocks in the front of picture are not level ledges but slope down to the right.

Many rapids form famous recreational areas for white-water rafting.

Rapids in Yellowstone National Park, Wyoming.

White-water rafting on rapids in Idaho.