I paddle board on my days off.
That's great exercise for your arms since you are using them to swim while lying, standing or kneeling on a paddleboard.
Yeah, but I get tired quick.
You can also try stand up paddle surfing or stand up paddleboarding. 
Thanks, i'll give it a try. What are the origins of paddle boarding?
In the early 1930s, Thomas Blake was given credit for the paddleboard construction.