Sentence:  There are many ways to go down a whitewater river. . . . If you paddle a play boat, you will play. If you paddle a more stable <WSD>river runner</WSD>, you may play a little less or a little differently. 
Meaning of the word marked with <WSD> tags:  A raft, kayak, or similar watercraft used especially for traveling with the current of a river in a swift manner.