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?
Whitewater
Whitewater is formed in a rapid, when a river's gradient increases enough to generate so much turbulence that air is entrained into the water body, that is, it forms a bubbly or aerated and unstable current; the frothy water appears white. The term is also loosely used to refer to less turbulent, but still agitated, flows.
The term "whitewater" also has a broader meaning, applying to any river or creek itself that has a significant number of rapids. The term is also used as
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