Sharkbreak
 

Follow the instructions and open the link below. It's Cool.
The fish follows your mouse, but there's more.

This is amazing, if you click on the extreme right hand column you can change the scene of the background. There are some really beautiful ones.

By clicking on the extreme left hand column you can change the type of fish, it's relaxing to watch them swim.

http://www.sharkbreak.com/