Boating
Four people out on an inflatable boat battling the foamy white waves. They could either be white water rafting, racing or just taking a boat ride through choppy water.
A person alone in a small boat leaning forward to row the oars.
A small animation of a person in a canoe, gently rowing.
Here's a pretty image of two sailboats sailing in the water at sunset.
Windsurfing
This is a small graphic of one of the more popular water sports, windsurfing.
This picture of a windsurf board is available as a vector graphic and a large transparent png.