It kind of depends on what he wants to fish for and where he will be in eastern Washington. I'm assuming he doesn't have a boat. Moses Lake and Potholes are great for bass. Blue, Park, Warden, and Quincy lakes are good for trout. These are just a few that are in Grant Co. If he is into salmon, the Columbia opens on the 1st of July.
I'm sure you will get some good info if you are more specific on location. Good luck