A body of fast moving water passing along a narrow channel?

A body of fast-moving water passing along a narrow channel is often referred to as a "rapids" or "stream." This phenomenon occurs when water flows swiftly through a constricted area, creating turbulence and often leading to whitewater conditions. The speed and volume of water can vary based on factors like gradient, channel shape, and surrounding terrain. Such environments are common in rivers and can be important for ecosystems, recreation, and hydropower.