I went paddleboarding here for the first time yesterday and it was an incredible amount of fun. The staff are great and very friendly. The paddleboard was $16 for the entire time (~2 hours) but I think they might charge you by the hour when it's busier.
They accept credit cards which was appreciated and only one member of the group had to show an ID.
We had free reign of the lake and went all the way over to the Terrace. You get to see views of the Capitol that you'll never get from the road. Highly recommended!
I fell in a couple of times after mooning people on the Terrace but, hey, that's life.
If you haven't gone paddleboarding before and have any anxiety - get over it and try these guys out - you won't regret it. Well, you might regret it, but that probably is indicative of a larger problem with your overall life outlook.