Rapids are sections of a river where the river bed has a relatively steep gradient, causing an increase in water velocity and turbulence. Flow, gradient, constriction, and obstacles are four factors that are needed for a rapid to be created.
Rapids featuring whitewater, close to the Rhine Falls
Violent water below Niagara Falls
Rapids on the Mississippi River (Ontario) in Pakenham, Ontario, Canada.
Historical image of the river rapids on the Maumee River in Ohio
A stream is a continuous body of surface water flowing within the bed and banks of a channel. Depending on its location or certain characteristics, a stream may be referred to by a variety of local or regional names. Long, large streams are usually called rivers, while smaller, less voluminous and more intermittent streams are known as streamlets, brooks or creeks.
Rocky stream in Italy
Frozen stream in Enäjärvi, Pori, Finland
Stream near Montriond in south-eastern France
Aubach (Wiehl) in North Rhine-Westphalia, Germany