I like to kayak in a small narrow watercraft in my free time.
Thats sound great. Kayaking is a very healthy activity. Where do you kayak?
Mostly on whitewater rivers.
What is a whitewater river?
A turbulent river.
That is rather dangerous, turbulence can pose a threat
a fluid flow, which overcomes the damping effect of the fluid's viscosity. For this reason turbulence is commonly realized in low viscosity fluids. In general terms, in turbulent flow, unsteady vortices appear of many sizes which interact with each other, consequently drag due to friction effects increases. This increases the energy needed to pump fluid through a pipe. Turbulence can be exploited, for example, by devices such as aerodynamic spoilers on aircraft that "spoil" the laminar flow to increase drag and reduce lift.
The onset
Whitewater kayaking
Whitewater kayaking is the sport of paddling a kayak on a moving body of water, typically a whitewater river. Whitewater kayaking can range from active, moving water, to demanding, extreme whitewater. 
History.
Paddling on rivers, lakes and oceans is as old as the Stone Age. The raft, the catamaran, the canoe and the kayak evolved depending on the needs and environment of the indigenous peoples in different parts of the world. The modern day kayak most likely originated about 8,000 years ago along