Do I need to know how to swim? YES!!! At the very least, you should feel comfortable and strong treading water. Chances are, you will fall in the water. The boards are incredibly stable and supportive, but we play...a lot! I encourage you to get out of your comfort zone and make peace with the river.
Is it O.K. that I've never done yoga or been on a stand up paddleboard? It's more than O.K., it's awesome! Look for the beginner specific classes on the schedule.
What if it's windy? Ah, The Gorge! The winds! SUP yoga and high winds make for an interesting outing. I want you to have fun and enjoy your time on the water so if the winds are not cooperating, we'll reschedule the class.
What to wear, what to wear? Definitely start with your favorite sun protection. Hats and sunglasses are nice. Bathing suits or yoga gear? Totally up to you! For the ladies, how will your bathing suit hold up in a Downward Facing Dog and how much time do you want to spend adjusting? If you're in a sunrise class or cooler temps, layers are good. Paddling creates heat!
Extras Keep it light. You don't need much. Bring a water bottle! Bring a towel (to leave in the car or on the shore) incase you go swimming. You may want to bring a camera. Think about waterproof bags or some other nifty trick for keeping your keys/camera safe.